One of the main reasons I go to talk therapy is because it helps me get better at recognizing my own moods and recognize the highs and lows of BP and the warning signs of an episode. Having an outside party (ie the therapist) can analyze and look at things in a way differently than you can, which can be very helpful. It also can feel good just to talk about your feelings with someone whose job it is to help you and not judge you.
On your first visit, the therapist will probably just want to get to know you and ask a lot of questions about your background, what doctors you see, what meds you're on, if you have any diagnoses, etc. Then in future sessions s/he will start getting more detailed. Maybe they will have you track your mood, and if you have a super bad day -- why? What triggered it? You might talk about that with them, and they will give you tools to deal with or prevent bad days.
I think you should go, even though you're nervous and don't really know what to expect. Therapy isn't for everyone, but I think you might be surprised to see what benefits will come out of it.