BBT is your basal body temperature.
Using a BBT thermometer, you take your temperature each morning
immediately upon waking - before rolling over, going to the restroom, getting out of bed, etc. and keep track of your temps on a daily basis. You can use
www.countdowntopregnancy.com or
www.fertilityfriend.com to chart your temps and they'll help you predict your ovulation based on your temps, cervical fluid, cervical position, OPKs, etc.
I highly recommend it - you can learn TONS more about it by reading
Taking Charge of Your Fertility or FertilityFriend has a 30 day trial of their premium membership and you can take lessons on how to chart your BBT.
Basically, your temp stays fairly consistent before ovulation, rises after ovulation and stays high until your next period. If you achieve pregnancy, it stays high - and sometimes reaches a third level of consistent higher temps - throughout pregnancy.
This is my first cycle TTC but I started temping right away because I found the book so interesting and wanted to learn more about my body and cycle. Some women find it very stressful and confusing - I find it very relaxing and easy to do.
Anyway, best wishes to you!