The general definition can be said that the Greek gods and goddesses were godly people that represented and held domain over certain things. Zeus, the god of the sky, and Hera, the goddess of marriage, are generally seen as the 2 "leaders" of the gods. Athena is the goddess of wisdom and battle strategy. Posideon is the god of the sea and earthquakes. Artemis is the eternal maiden and is the goddess of the hunt. Apollo is the god of the sun.
That's a pretty general description but if you need more, feel free to ask.