Birth control "period"

Karla • 26. Married. Momma to 2 baby girls ❤️
So I'm on the pill and I'm just confused because I thought I was getting a period but I read that it's not really a period when you're on BC. I'm confused. Then why does it feel like a period?! And don't our bodies need to get rid of the uterus lining? What's "blood withdrawal"? That's what i read on the article. Does anyone know how to explain this? 
Sorry too many questions