Background on me: I am a classically trained trombonist who struggles with music theory.
I know that a trombone is in the key of Bb, but what does that mean? The key is determined by the piece your playing? Additionally, a trombone with an F trigger is shifted into the key of F when the trigger is depressed (same with the G trigger on bass trombone). What does that mean? For me it just means that first position is now 6th.