Here are the main basics of learning to drift.
Drifting may seem hard at the beginning, but trust me it is worth it.

Where do I start?
The first step to drifting in games such as Assetto Corsa, is you want to make sure you have a steering wheel. Any wheel is fine as long as it supports a proper H-shifter or a sequential will do.
The wheel I am using/started with is a Logitech G920, which you can use as a starter.
I highly suggest saving up and getting a Thrustmaster wheel rig if possible!
When buying a Steering rig, make sure you actually get the peddles that come with a clutch, this will be needed so that you can clutch kick, for cases like, needing to rev up as the rpm's may be too low, or to kick the rear end out that small extra bit.
Once all that has been taken care of, we can now go to the next step.

The next step
is actually getting the game you want to actually practice on, in this case we are using Assetto Corsa.
Now, for a game to practice on, I would mainly choose Assetto as it is one of the closest games to irl drifting.

Now for the next step.
Once you're in the game you want to practice on, you may need to setup the wheel, peddles and shifter so they're set up for better out comes.
Changing some of these settings may be a bit hard at first, but once you get a feel for things and know what works best for you is where you can properly start drifting.
Now, it took me a while to get my settings right for me but in the end, it was all worth it.
Don't just try one thing and say that it is the best for you, actually go into the settings and mess with them for a bit and try to see what works best.

Once all that has been completed, we can now go to the next step.
Now, you're probably thinking, what car should I practice in.
Any car is fine as long as it has enough power to spin the rear wheels and get you sideways.
Each car has different handling, this may be a little bit confusing at first but you will get use to it.
First, Make sure you're not in a high powered car, as using a high powered car in the beginning may make it a lot harder to learn about how the cars work and what habits you should and shouldn't keep doing.
Once you've picked the car, you are going to want to start. Any map is fine.
In this case, I would just go onto the map called 'Drift'. We can download more later on but this is the main one for learning.

Now here's where you actually learn to drift.
Take a few laps around the track and get a feel of the car with your steering wheel to make sure everything feels like it is working correctly.
Once you know it is all good, this is where you can start drifting.
Now don't go all crazy and instantly think you can do it straight away, a lot more than that goes into drifting.
Come up to any corner of the map - at a good speed, depending on the car, I would do about 50-60 km/h, this also depends on the length of the turn. The longer and wider the turn, the more speed you'll need, smaller the turn is the opposite.
If the turn is a long and wide turn. Pull the handbrake and then go into the turn and start counter steering as soon as you feel the wheels beginning to slip, which is one way of initiating an entry, but don't use your handbrake all the time - not only does it slow you down a little but in competitive drifting can decrease your scores.
When you come up to a turn - you will want to come out a little then go towards the turn and then pull the handbrake, which will bring the rear of the car out.
Do not forget to start counter-steering as soon as you feel the rear wheels slipping. Don't counter it too much. Counter it depending on the angle you're getting and try to balance it, as if you're trying to counter a vehicle on two wheels.
Practice doing that a few times and then you can start the next step.

This is where it gets a little bit harder.
Once you've learnt to do the simple handbrake entry, now you can practice counter-steering.
To do this, you are going to do the entry initiation that I explained earlier.
Once done you can now let go of the steering wheel but keep your hands close to it as you are going to need to catch it, let it go around until it feels like the car is just about to loose traction.
You are going to, counter-steer, to do this you will try to do slight adjustments to the wheel. Depending on how much angle you are at, for example, if you are facing too far in, try steering to the opposite side you are facing, and if you feel like you aren't getting enough angle - there is a few ways you can fix that. The first one is by using the handbrake to bring the rear end out more, or we can try to do a scandinavian flick (Turn away from the corner and then turn back towards the corner without using the handbrake. Doing this in the correct pendulum motion will cause the rear end to slide out. You can also clutch kick into a corner!.. We are also going to apply a bit more throttle when we are getting sideways which is where the next step comes in.

Throttle is a big thing with drifting.
It isn't just about the counter-steering and the entries, it is also about how you use the peddles, for example when coming up to a turn you may want to use your brakes to slow down a little, but don't use your handbrake to slow down as that is only to bring the rear of the car out more.
Learning throttle, braking and clutching, aren't the easiest of things, but it is worth learning.
If you're just about to switch gears, make sure to clutch in just before you do it, then you switch to the next gear, or to the lower gear.
This is also needed for things like takeoffs on the spot, handbrake entries, clutch kick entries, low rpm's and many other cases.
One thing you want to make sure of is that you are not trying to be a crazy driver and go to fast, you're actually going to want to slow down just before a turn, and then use the handbrake, this will also stop you from coming into the turn to fast, causing you to spin out, miss the turn, or go to wide.
Enough of that stuff, now you're still needing help with the throttle, try to get a feel for the car, dont constantly sit on the throttle, what you actually want to do is if your car is not getting enough angle, not only turn in a little bit more but also try using a little bit more throttle, as it causes the rear wheels to spin quicker, meaning the rear end of the car will flick out more, and to do this if you are getting to much angle, it is pretty much the opposite, just use less throttle, counter steer opposite to the turn more, and you should be able to hold the drift after that.

Now, with all of these basic steps, you should be able to start drifting for the first time.
Yes, I know reading this may of taken a bit of your time, but trust me, it is worth reading this rather then just going in without actually knowing what to do.
Hopefully this helped everyone. I spent a lot of time Typing this....
But I've always loved helping people with things, and when I help people I try to explain to them in detail on how to do something.
Now, if this did actually help you, please Rate this guide.

There will be more Guides coming soon, with me explaining how to transition and all the advanced things.

If you would like to see what it took, for me to get to where I am today, you can click here and goto my Youtube channel.
https://www.youtube.com/channel/UC333UgPKQK4J7zo9YbcJGNg
On there, you will see what it took for me to properly learn to drift. New videos are coming out soon of me drifting but they may take some time as my upload speed isn't the best.