The Coccinellidae is the family of beetles that are known as ladybugs (or ladybirds). There are over 5,000 species described in this family. Almost 450 of those are native to North America. Beetles in this family have wing covers that are yellow, orange or scarlet with small black dots. However, it should be noted that a lot of the beetles in this family are in fact entirely black, gray or brown. In fact, it may be difficult to recognize many of these as ladybugs.
The ladybugs in general are useful insects for humans because they feed on aphids and scale insects. In many places in the US you can buy hundreds of ladybugs in jars to release into gardens as pest control.