Mini pill help!

Laura • Laura, 20, in a happy relationship 2 years TTC #1
I'm on the mini-pill and to be honest I don't have a clue what it does?? Can someone please help me out, I'm having a lot of unprotected sex with my boyfriend and he hasn't being pulling out. I was just wondering if this could get me pregnant?? Someone please tell me how affective the pill is?