Post a request for software you need built, or claim an open request and build it. Developers can hold up to 3 active claims at a time. Posting costs nothing on top of your budget, the 12% + 75ยข platform fee comes out of the developer's side when you approve the work.
When somebody needs software built, it appears here for developers to claim. Post the first one, you set the budget, and it stays in escrow until you approve the work.