From what I could understand so far:
It's a platform for artists, kind of a mix between Instagram and Deviantart (you can join as a "non-artist" and share text posts only, though... I don't really see the point of doing that, tbh? XD).
Your profile page can be customized with an avatar (obviously) as well as a banner and a color of your choice (from a limited palette). You also get two "bios": a short one that shows right under your username, kinda like what you get on Instagram, and a longer one, where you can also add links to your websites. Yep, you can have multiple links in your profile... and under posts too, apparently.
Posts are of two kinds: text posts (which I haven't tried yet) and image posts. Images can only have three hashtags, BUT unlike Instagram, there are also categories under which you can post your art. There aren't a whole lot of them available, but say... if you post under "landscape", your artwork will automatically show up under that category, so you won't need to add #landscape as a hashtag for your post to be seen XD
The two main reasons why people are talking about the site so far seem to be: a. challenges (basically the same you usually see on Instagram, only that on Artfol they get a dedicated category, with specific sub-categories for challenges and for challenge entries) and b. the fact that posts show up in a chronological order rather than being sorted by an algorithm, which means more chances for small accounts to be seen. The atmosphere seems pretty chill so far, and the chronological thing kinda reminds me of Pillowfort, which I'm sorely missing after their epic fail of a launch XD
Haven't experimented much with it yet, but it does seem pretty nice. Not a fan of the fact that it's mobile-only, though... and the lags are definitely annoying XD
Edit: oh, there also seems to be a space for commissions! Not sure how it works exactly, but I've seen the "commission" button on a few profiles... I'll have to look into that!