In Ancient Greece they had a very different religion than we have today. They believed in gods and goddesses, they thought that these gods and goddesses could effect their life in a good way or bad. In order for the gods and goddesses to give you what you wanted you had to honor and worship them. So they did just that.
Each god and goddess had power over something, normally nature but it could be love, war stratagy, etc. According to the Greeks some of the god and goddesses that ruled over nature are Zeus, Demeter, and Poseiden. The god Zeus ruled the sky and threw lighting bolts, goddesses made the crops grow, and god Poseiden caused earthquakes. There were 12 god and goddesses that were declared more important than the rest, these select few lived on Mount Olympus, the highest mountian in Greece. Among the 12 were Zeus, the chief god; Athena the goddess of wisdom and crafts; Apollo, the god of sun and poetry; Ares, the god of war; Aphrodite, the goddess of love; and Poseiden god of seas and earthquakes. The Greeks also believed an afterlife, after you died you would go to the underworld ruled by the god Hades. It was not a good place. The Greeks also believed in fate, that you had a set future/path. To know what your path was Greeks visited an oracle. A person who supposedly could predict the future and tell you abouth your future. Although thats not all an oracle could tell you, they also told prophecys. A prophecy was when a god or goddesses sent a sign to forewarn you of something.
As a result of these beliefs Greeks built temples and buildings in honor of the god and goddesses, they wanted to please them. The greeks also went to church often to show their respect for the god and goddesses. The greeks worried about their every move wondering, "Will the god and goddesses like what I just did? Or are they mad?? Oh no, will they punish me? What can I do to make them happier??? Uhhh..."