You kinda got it, not far off!
You get paid when people download your files. Sorry, I can't find teh page with details on right now, if I find it I'll post it here!
If you want to promote the app itself you need to sign up as an affiliate at http://www.gygan.com/affiliate/
. Don't worry if you don't hear back from them straight away, seems to take a while for applications to be processed.