The placebo pills usually contain iron or other inactive ingredients, and do not contain any hormones (though in some brands, they might contain very low amounts of estrogen). During the placebo break, you have a monthly withdrawal bleed (it’s not technically a period, since you didn’t ovulate). You don’t have to take the placebo pills, but they’re in your pack to remind you to keep taking your pills at the same time every day. You’re still protected from pregnancy during the placebo break, as long as you’ve taken all the previous active pills correctly.
You might not start bleeding until a few days into your placebo break; this is normal. Be sure to take the first pill of your next pack as soon as your placebo pills run out, rather than when your period ends, to maintain pregnancy protection.