One song:
A whole list: on the Songs page open Add many at once. Paste one song per line as Title | Key | Tempo | Composer (only the title is needed), or choose a .csv or .txt file. A CSV needs a header row like Title, Key, Tempo, Composer, Notes. Press Add them to the library. Songs already there are skipped. Attach charts to each song afterward.
Players can open a song's charts from their offer page when the song is in that gig's set list. Players who turned the gig down can't. Only share music you have the right to share.