What breed and how old is she? There is always a chance she might reject them but some breeds do better than others.
First off you want her to be broody for a while, I would wait at least 2 weeks before introducing chicks. Move the broody's nest to a separate little area with food and water (it can be a fenced off section of the coop) so she can be penned in with the chicks for the first 2-3 days. You don't need to keep her locked up while she is sitting, but you will want to close off the area when the chicks arrive.
The chicks you give to her need to be very young, usually 1-2 days of age. Put the chicks under her at NIGHT! Let her feel them moving and "discover" them in the morning.
Next morning get up early and see if she accepted them, if she doesn't drive any out of her nest you are probably good to go. I usually offer up a bowl of scrambled egg the next morning to get her eating at the nest site. If for some reason she doesn't accept them be ready to raise them yourself.