For online rehearsal aids, see here.
Musical Terms: Glossary of Common Terms. Alternatively, aimed at younger choristers, but useful for all of us, a Musical Glossary for Kids, which also contains an excellent link on musical acoustics, if you scroll down to the bottom. Our thanks for the latter to Graham Hathway in Maine USA, quite possibly both our youngest and most distant website user!
Musical notation is usually in Italian, eg piano, softly, because most early composers were Italian.
See here for common Italian musical terms, together with their meanings.
For guidance on pronunciation, see the video below. (Don’t be put off that it starts in Italian! It switches to English very quickly):
Alphabet (with audio)
Pronunciation, Diphthongs, Consonant Pairs and Dangers to Avoid
Pronunciation of Ecclesiastical Latin
Voice training available online
Music theory can be learnt online, see here and here.
See Sound Gym or EarBeater.