Hi, Todd -
Sorry about your having to sing to recordings - background tracks are OK but I prefer live :-)
As a fellow instrumentalist I know it's a big switch. Singers tend to focus on something called "blend", that is, they don't want any one voice to stand out too loud from the group (unless it's a solo). So it's a good sign that you're accepted - you must be doing somthing right! Keep on with it, things will get better with time.
Now about your questions - Voices can either be high (tenor for guys, soprano for gals) medium (baritone/2nd.sop) or low (bass/alto). Each person has a high (head) and low (chest) range. The border between these two ranges is called the "break", kind of like the difference in tone between your highest and lowest strings on the bass. If you ever listen to some old Quartet recordings on YouTube or similar you might hear examples of this. Falsetto is a type of "head" voice that tenors use to get up into their highest notes. You'll notice when some of those guys do that their tone sounds 'light' and thinner. That's head voice. And a type of growly voice Basses use to scoop out their lower notes - that's "chest" voice.
Melody is the words/notes that most people sing - like "Someone asked the question" in Kirk Franklin's WHY WE SING. Harmony is when his backup choir breaks out with "I sing because I'm happy". Sopranos end up with the melody, mostly, with tenors doing it sometimes - but altos and tenors usually get the harmony parts, with basses taking up the bottom. Most Gospel music is 3-part SAB (soprano, alto, baritone/tenor). If you cannot find your part right away, a good strategy is to find the melody, unless someone else in your group wants to teach you a harmony part. But as a Bass player you might be able to pick out a bass line for yourself if your voice can get down there...
