I have a question that I seriously want a answer for! The doc says I'm 1cm 50 effaced -2. What does -2 mean?? I'm so clueless

Thanks for all the ❤️ guys! I think I'm in shock! Labor story in a bit I'm being attacked with visitors lol
guess what!
I just joined the June 2017 month!! Eep! Exactly 2 years ago, I was finding out that I was pregnant, and 2 years later, I'm finding out again!! I'm so excited!
Ok I'm 15 And Pregnant And I Don't Know What To Do. I'm Just A Freshman In High School.
I Guess I'm about 2 start labor