1st Achievement: "First Day"

Complete your first level
Details: Go down by using the safehouse elevator and collect supplies around the studio. Every items are different and randomized for each day, especially on every floor. But since it's your first day, your floor is "Studio". Here's a list on Items you would be going through.
Supplies:
1. Wrench
2. Book
3. Radio
4. Plunger.
5. Bone
6. Gear
7. Spoon
You'll see what you need to collect on the left side of your screen. Collect and bring them back to your safe house before the Ink Demon gets you.

2nd Achievement: "Forever Tomorrow"

Visit The Chair that Spins
How to get it?
Explanation: Next to the Safehouse Elevator, there's a door once you open, you can explore more mysteries in the safehouse. Go down until you see a Bacon Soup Station and keep on going right until you see "Golden Days Gallery". Enter you'll see all art from different artists, even a Lost one is there just wants to look in peace. You'll also see a chair and interacting with it, it spins and you got the "Forever Tomorrow" achievement.

3rd Achievement: "Paper Chase"

Discover the secret of the Safehouse Scraps
How to get it?
Explanation: In "Studio" floor, there's safehouse scraps in the lockers. You'll have to find all 7 of them. But you won't find them all in one day. Some are there in one day, the next day they aren't any. Grind for a few days (in game) and you'll get them all. Once you do, go back to the lunch table safehouse, you'll see a stove and next to it there's all the scraps that you collected. Interact with it and you get the "Paper Chase" achievement.

4th Achievement: "Technical Terror"

Defeat your First Boss
How to get it?
Explanation: after unlocking some floors and progressing the game. (You don't need to unlock all floors yet for this one). Pick the floor for the next day but you'll randomly enter a boss fight with a robot counterpart of either, Bendy, Alice or Boris. When you are in the boss fight, fight back and block attacks from the robot. Don't let it run away and regenerate. Defeat the boss and you got the "Technical Terror" achievement

5th Achievement: "The Bertrum Special"

Unlock the Arcade
How to get it?
Explanation: when you defeat the boss fight for the first time, the robot will drop something and that something is a key to the arcade. Go back to the safehouse and kinda go to the same directions that you are going to the "Golden Days Gallery". But this time, you'll see a door to the arcade, unlock it and you got the "The Bertrum Special" achievement.

6th Achievement: "Light and Dark"

Escape the Monster of the Abyss
How to get this?
Explanation: In the "Abyss" floor, you'll need to find 5 ink hearts. Again, it'll be randomized. Once you find all 5, go back to the safehouse and outside the elevator room where you see your "Progress Saved". Go left and you'll see an inky heart. Interact with it unlocks the "Projectionist" level. Complete the level by finding all 6 hearts and you get the "Light and Dark" achievement

7th Achievement: "Pest Control"

Defeat 50 Ink Widows or Flyers
How to get it?
Explanation: for this achievement, all you gotta do is kill 50 Ink widows or Flyers. They're all over the studio floors but they mostly spawn more in deeper levels like the "Aybss" and "Lower Levels" and etc. Kill 50 and you got the "Pest Control" achievement

8th Achievement: "Banjo Boris"

Play the Banjo in the Safehouse
How to get this?
Explanation: In "Music Department" floor, you'll need to find the Banjo in one of the coffins. It'll be randomized as well, collect one and finish the level. Once you collect the banjo, go to the safehouse and the Banjo is near by the kitchen stove. Play the Banjo once and you got the "Banjo Boris" achievement

9th Achievement: "Repairman"

Unlock All Floors
How to get it?
Explanation: To unlock other floors, you'll need to look for "elevator buttons". Not all buttons are in one level, there's one button for each floor. To show how it works here:
Studio = Artist Rest button
Artist Rest = Abyss button
Abyss = lower levels button
Lower levels = Music Department button
Music Department = Tunels
Tunnels = Gent Workshop.
Once you find them all, you got the "Repairman" achievement.

10th Achievement: "Sad Lies"

Escape the monster of the Lower Levels
How to get it?
Explanation: To get this achievement, you'll have to go to the "Lower Levels" floor and find dead boris clones that has audio tapes by Milla. You'll have to find 5 of them and when you have all 5 of them, the last thing that you need to do is to find a key to open the door. To find the key, you'll have to look for it in a dead boris clone. Once you got the key, go back to the safehouse and pass the Fuseball game, you'll see a small room that has Milla audio tapes and the door. Now, you unlock Alice Angel level, complete it by finding supplies and you got the "Sad Lies" achievement

11th Achievement: "The Believer"

Complete the Music Department
How to get it?
Explanation: In "Music Department", you'll have to find 4 candles that are in the coffins It's randomized as well. Collect all 4 candles and the last one you will need is Sammy Lawrence mask. It'll be inside of one of the coffins as well. Go back to the safehouse and head over to the guys restroom. There inside you'll see the candles and the mask. Interact with it and unlocks "Sammy Lawrence" level. Complete the level by playing the correct notes and you got the "The Believer" achievement.

12th Achievement: "Forgotten Days"

Unlock the Gent Laboratory
How to get it?
Explanation: In "Gent Workshop" floor, find those little locker, (Not sure the name) but you'll find the Gent key, it's also randomized as well. Once you collect the key, go back to the safehouse and go past the females and males restroom. There's a GENT sign and the door, unlock the door and you got the "Forgotten Days" achievement

13th Achievement: "Butcher Butcher"

Defeat 25 Butcher Gang
How to get it?
Explanation: To unleash The Butcher Gang, you'll need to find 5 Padlock keys on floor "Studio" It'll be inside one of the lockers. Once you collect all 5, go back to the Safehouse and go down until you see a long crate. Unleash The Butcher Gang and kill 25 of them and you got the "Butcher Butcher" achievement.

14th Achievement: "Hide and Creep"

Complete the game in the Tunnels
How to get it?
Explanation: In "Tunnels" you'll have to find 5 handprints. The handprints aren't hiding, just you have to look for them the same way that you are finding the supplies. Once you got them all, head over to the "Golden Day Gallery" and you'll see a handprint on the wall. Interact with it and unlocks "Porter" level. Complete the level by finding Heidi 3 times and you got the "Hide and Creep" achievement

15th Achievement: "Mister Astaire"

Collect all the safehouse Dance Steps
How to get it?
Explanation: In "Music Department" floor, you'll have to find 6 Dance blueprints in the restrooms. It's also randomized as well. When you find the last one, you'll get the "Mister Astaire" achievement

16th Achievement: "Fuse Collector"

Score 25 Points in Fuseball
How to get this?
Explanation: In "Artists Rest" floor, you'll need to find all 7 fuses. It'll be inside those fuse machines. Get them all and go back to the safehouse. Outside of the elevator room, there's the fuseball game. Score 25 or higher in the fuseball game and you'll get the "Fuse Collector" achievement

17th Achievement: "Survivor"

Complete the Main Story
How to get it?
Explanation: To achieve this, you must finish all your things on the process list next to the supplies box.
1. The Safehouse Scraps
2. Fuseball
3. The Projectionist
4. Alice Angel
5. The Butcher Gang
6. Sammy Lawrence
7. Porter
Once you complete them and open the GENT in safehouse, there's one more thing you have to do. Which is to find 5 "Gent Schematic" by destroying the turrets in "Gent Workshop" floor.

18th Achievement: "Fuzzy Friends"

Collect All Plush in the Safehouse
How to get it?
Explanation: In the Arcade, there's a claw machine filled with plushies with Bendy and other cartoon characters. To play, all you need is coins that are called "Slugs". The slugs are all over the studios floors. Save them while you are getting supplies. Here's a list to collect:
1. Bendy
2. Alice
3. Boris
4. Charley
5. Barley
6. Edgar
7. Carley
You don't have to collect the mystery plush since you can get the achievement without it and it's not obtainable

19th Achievement: "Golden Record"

Collect all the Safehouse Tunes
How to get it?
Explanation: In "Music Department" floor, you'll need to find all 6 Safehouse Tunes in lockers. Find them all and you got the "Golden Record" achievement

20th Achievement: "Wolf Forge"

Unlock All Weapons
How to get it?
Explanation: To achieve this, you'll need to find all weapons in GENT weapons crates during your days hunting supplies. GENT weapons crates are all over the studios floors. Destroy them and a weapon will be giving to you randomly. Here's a list of the weapons:
1. Frying pan (giving to you at the start)
2. Plunger
3. Baseball Bat
4. Mallet
5. Scythe
For the Scythe one, I heard it's weird to get but you need to unlock the ink toy from the dead Boris clones and setting to the ink machine and unlocking the 7 mystery boxes. Also it's a low chance of getting, it can take like hours to get it but if you are lucky, you can get it early so you don't have to grind hours on it.

21st Achievement: "Steel Boris"

Complete the Main Story on Hard Mode
How to get this?
Explanation: To achieve this, you must play and complete the main game on hard mode. Once you do, you'll get "Steel Boris" achievement