With most pills, you can start taking it in one of two ways: Day 1 start or Sunday start. If you start taking it the first day of your period (Day 1 start), it is effective right away. If you start taking it the Sunday after your period starts (Sunday start), then you have to use a backup method of birth control (condoms, foam, etc.) for the first 7 days of the first pack. After that first week, you are then protected, provided you took those first 7 pills correctly and on time. Some women, though, like to use backup for the entire first pack just to be safe. As for breast growth, that's a very individual thing. Some people will experience growth, while others don't, everybody is different.