What is the effectiveness of birth control?

I have a few general questions about birth control since I started about 2 weeks ago:

If you stop taking your birth control for a week would that be the same as being on the placebo pills?

Can you get pregnant while on the week of placebo pills?

How does missing 2 days worth of pills make bc less effective if being on placebo pills that contain 0 hormones doesn't change the effectiveness?

How does a period work on birth control? --> does it come while I'm on the pill or does it come after I start taking the placebo ones?