HELP NEED ANSWERS

I have been taking birth control for about 6 months now and I’ve heard that u have to wait around 7 days for it to be effective and protect you from having kids. But I’m confused does that mean for every new pack I start after my period I have to wait around 7 days for birth control to be effective. Or when I start a new pack am I good after the first pill or 2 I take and it’s in my system ??? I’m confused. I started a new pack 3 days ago and have takes 2 of the active pills on the top row and had sex today but with a condom as well.