FA a lot more barebones than dA, but I will do my best to explain the folder thing:
To setup a folder you need to do it from the upload page. You can then edit them on the Folder Management page on your settings. You can create groups for your folders as well on that page. Here's how mine look in my gallery for example (I use the old FA layout but hopefully it's still easy to understand)
Another thing you should know is that, unlike dA, you cannot hide certain images from your main gallery, even if you put them into folders. They are there more so for personal organization. The only submissions that don't show up in the main gallery are your Scraps.
Also I should warn you: FA currently
does not have a protection for AI harvesting bots. (at least not as far as I know) Please be aware of this before you start posting.
If you have any other questions about the functionalities of the site, you can ask! Like quoting_mungo said, there's no right or wrong way to use the site. The only thing that I recommend is always set the right Maturity Rating.
[Edit: I see Inferndragon already did a more in depth tutorial above haha]