Can you read music? If so, Get a hymn book and break down the notes. On the treble clef, the top note is Soprano, the lower one is the alto note. On the bass clef, the top not is the tenor note, and the lower not is the bass note, which you will probaly disregard when it come to the choir.
If you practice that maybe it will help.
Also, sit in one another choir's rehearsal, and check out what they do, or join a community choir
I'm learning how to harmonize too, I can often hear the alto note, bu have a hard time finding the tenor note.
