Basically it's an app that let's join and create fan forums/communities of anything you love and have interests in such as anime, cartoons, comics, movies, video games, etc. You can make posts of fanart, reviews, videos, or you can chat with other fans on the forums. I highly recommend getting the app on your smart device if your into those kinds of media.
P.S. I have an account on Amino, it's SilverCrystalGem95
I'll list which Amino's I'm apart of in the near future.