New here want to introduce myself

Options
Hi ladies :) My name is Bridgett and I just had a little boy 3 months ago on April 24th. This is my second boy.
I gained 27 pounds with my pregnancy and have lost all but 10 of that, but my main issue is that I was already overweight prepregnancy due to my first pregnancy 4 years ago. I REALLY need to lose weight to feel better about myself and to be healthy for my kids.
So how does MFP work? I mean I understand how everthing works, but if you follow the calories it gives you per day, you are guaranteed to lose weight? OR what is the best way to use MFP to lose weight?
Thanks!
Feel free to add me.