Click on the Forums (globe icon) in the top left corner of the iReal Pro window.
This will open the forums in your default browser where you can choose a music genre.
(Jazz, Pop, Latin...)
Choose a conversation thread with the playlist or song you want, for example,
Jazz 1350 Standards
Click on the link in the post, for example Jazz 1350
The songs will import automatically. You don't need to be registered or logged in to download songs.