Ancient Greeks were polytheistic meaning they believed in many gods. The gods had believed to be anthropomorthic or having human feelings. They could be angry, sad or happy. Ancient Greeks sacrifaced meat to the gods before every meal that contained meat. They thought if they did not sacriface meat to the gods they would be cursed like when Odysseus, the sacker of cities was cursed by Poseidon, the god of the sea and horses. They feared they would have bad fortune.
Ancients Greeks also thought olive trees as sacred, a person would be killed if they cut down an olive tree. People used oil from olives as well as the olives for many things including to bathe, to cook and wash their hands . Ancient Greek religion and present Greek religion are different ;today Greeks are mostly Greek Othordox. They no longer believe in all of the gods however; they still use olives and olive oil for cooking just like in ancient Greece