Vaginal Tearing

Ok, so I am only 6 weeks along with my first baby & have never really been too nervous about birth until I have started to hear about horrible tearing that can happen during a natural birth! I mean I understand the 1st and 2nd degree tears but 3rd and 4th degree sound absolutely terrifying. How often do those really happen? With your first baby, what kind of tearing did you have? Small or intense?