Now, if you are really new to this (and I mean like literally just discover that you can upload custom artworks) then there are things that you should know when designing your first profile artwork.
First, your account need to be at least lvl 10 so you can showcase your artwork. Second, there are 2 types of artworks, Long Artwork and Short Artwork; and don't worry, I've brought pictures. (That isn't mine, I found them on google images and so I do not who these people are.)

[If you are using the short artwork template, you can skip this step]

Like I mentioned, most people prefer to use the long artwork template and if you are one of those, you should also know to upload your file as a long artwork. This guide will go more indept and does a much better job explaining on how to do that; for me, I will only going through the simplify version.

For uploading a long artwork, you cannot do it within the Steam client, you have to do it on a browser of your choice, be it Chrome or Firefox. Copy and paste this url into your browser: https://gtm.steamproxy.vip/sharedfiles/edititem/767/3/, it will take you to the Upload Your Artwork screen.

It should take you to this screen:
After that, put in the image that you have prepared, name it, and then open up the console by right clicking anywhere then click on "Inspect Element" or press F12 (work just as good).

After you've opened the console, click on the console tab as shown below.
Then all you need to do is enter this command: $J('#image_width').val('1000');$J('#image_height').val('1');

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After you've opened the console, click on the console tab as shown below.
But before you can copy and paste in the command onto the console, you need to do something first.
What you need to do is to type allow pasting into the console and delete it right after (you don't need to press enter after you've type that).
doing that will let you copy and paste the command into the console, and the command that you need is right here:
document.getElementsByName("image_width")[0].value = 999999;document.getElementsByName("image_height")[0].value = 1;

After that just upload the image normally, and just like that you got yourself a long artwork. For short artworks, you can just upload it as it is and not have to go through this process.

Now that we got that out the way, what comes next is the juciest part of this process, it's the designing process. A good way to start is to go to Steam.Design[steam.design] to crop out the background of your choice (you can only use the backgrounds that you own). Just download the .zip file for it after you're done with the cropping.

Open the download folder (or wherever you've download it to) and move the following files: Artwork_Middle, and Artwork_Right_Top (Avatar is also optional) to the desktop for easy access.

However for this process, I'm going over the easiest way that I've discover to make some low effort artwork by only adding stuffs to Artwork_Middle, though you are more than welcome to experiment with Artwork_Right_Top and Avatar if you want, who am I to stop you.

Start by opening Artwork_Middle (that you should have on your desktop) in Paint3D as shown. You do so by right clicking on the file and then click on Paint 3D.

After you've opened it, you can start the process by going to the Stickers tool and the option to upload a custom sticker.

Next, is the choosing what you want to put on the foreground, it could be an anime character, a logo, or even a meme, but whatever it is, it has to be a .png file or it will not work. Drag it around a little, find where you'd like to put it.

When you've find that perfect spot for your character, simply click the check mark to comfirm it.

The last thing you need to do is to save it as a seperate image in your hardware,
you can also rename it to what ever you want for easy finding.

The only things for you to do now is to follow the steps I mentioned in The Basics (continue) section to upload this as a long artwork (remember that you also have to upload the Artwork_Middle file as well as the Artwork_Right_Top), if you wanted a short artwork on the other hand, just upload this as is it (though do check for the correct resolutions, you can change its resolutions in Paint 3D).

Edit your profile, choose the correct background, pick the corresponding artwork, and save.
What you have now is your very own artwork that you worked so hard on.

That was what I believed to be the absolute most basic way I could create a profile artwork. I'm personally is still trying to learn how to make mine better and I am in the process of creating a similar guide but on GIMP instead because I'm too poor for any of the Adobe programs. This guide is mostly targeted towards the newbies rather than the veterans, since like I said, these are pretty basic infomations. I thought it'll be helpful for those people to know this before they start to venture deeper into the pool.

So I would really appreciate you leaving a constructive critism on what I didn't mentioned/could've done better, or tell me something that I spelt wrong if you're a gammar police. >:3
Also, I will do my best to answer any questions you might have about this guide.