Hi CyclingLindy! Welcome to the forums. Glad you like the Downtuba (aka DT on the forums). A lot of us have them here. The President of the company, Yan, is quite responsive to any issues. I have the same color as you as well as a white one too.

To answer your question the BB is the bottom bracket which is the bearing that holds the crank (where your pedals are attached). Hopefully that helps.