I’ve never used it myself, but the TL;DR is that it’s supposed to be basically like Patreon, except that:

• it is itself a non-profit organization that funds itself via donations to its own account instead of taking a cut of the payments to others,
• its software is Open Source, and
• it only allows donations to creators (i.e., creators aren’t allowed to provide rewards in exchange for the payment – apparently, this is at least in part to avoid having to charge VAT).