I'll let @mvanhalen answer you but essentially it's the control center for all NFTs on the DESO ecosystem.

You can create, bid or buy NFTs there as well as create more complicated DeFi mechanics in tandem with the your NFTs if you so wish.

Glad you made it across!

If you haven't already, swing by @DeSocialWorld where i'm posting from right now so that you can take a look at what some other apps look like on the DESO blockchain.