Well if you start birthcontrol the first day of your period your usualy protected right off, but if you start after your period i beleave you have to use other forms of protection for a week.

I think most birthcontrols say to use a back up birth conrol(condoms) for the first week or two weeks. Read in the directions to your birth control to double check

You actually have to wait a month (until your first period after you start taking them) until you are full protected unless you start taking your pills on the same day that you start a period (then you are protected right away). Although, it is still recommended that another form of birth control (condoms, etc.) are used as well as staying on time with all of your pills.