If you bought black sexlink chicks that were all black except for a small patch of white on the back of their heads, you bought the cockerels.
If the backs of their heads were solid black, they are girls.
They are usually a Rhode Island Red and Barred Rock cross. Each hatchery has it's own particular lines and combinations of breeds. Hatchery birds are bred mostly for a high production rate. Temperament is rarely considered, so understand that they might be outgoing and want to be around you all...
Most hens are not human aggressive at all. It's roosters that get a little too territorial that become aggressive. If you want to guarantee only hens, a sexlink is the best way to go. Black sexlink girls are all black at hatch, some may have a bit of white on their necks. A red sexlink girl will...