The great news is that once you join a choir, the director will be able to tell you where your voice will fit best. Yes, your speaking voice will give that away. So you don't have to know that ahead of time. If you have never sung harmony that is notes that are not the tune, then you will learn. Don't be hard on yourself. Be patient. All in good time.
Here is a fun video that will give you some pointers about singing harmony. I love his explanation of harmony being a number of melodies sung at the same time. Enjoy. See it isn't nearly as scary as one might think.