If you're an end user who is actively looking for an IMAP e-mail client, please note that Trojitá's GUI is not completely ready for mass consumption yet (read: needs some polishing to not scare users away). If you are scared now, please come back in a few months, you might be pleasantly surprised :)
Please see the download page for details about how to obtain, compile and run trojita.
The most comprehensive reading about trojita is undoubtly the bachelor thesis. It discusses design of the application and provides a comparison with various other mail user agents.
A series of blog posts about Trojitá might provide an interesting insight into its background, too.
If you encounter a bug in Trojitá, please report it to it's issue tracker.
Wishlist items belong to the same place.
Trojitá's IRC channel #trojita is hosted on Freenode network. The main author, jkt, is often to be found there.
There's a mailing list trojita@lists.flaska.net. You can always contact the author by e-mail. However, issue tracker or the mailing list is the preferred way for reporting bugs and requesting features.