Ok, start writing your proposal. Donors Choose gives you a lot of help here. They have samples of great proposals and they give you pretty clear directions. I always write like I talk. So most of my proposals come across as rather old Brooklyn, but hey that's who I am.
Right before you submit your proposal, they give a chance to see what it will look like live and to make any last minute corrections. It's very easy to navigate between pages, and the process has been streamlined a lot. It's much more user friendly now.