The reason behind Greek mythology

Natural phenomena
What is rain? Why does it rain? Surely you know the answer that water evaporates from seas, lakes and trees it forms moisture at an altitude and condenses to form larger drops which are heavy hence fall as rain.
Our knowledge about rain is no more than 500 yrs old. And yet it has been raining for millions of years ! Then how did people living 5000 yrs back explain this phenomena?
You may say that people then would not have attempted to explain it, then you would be wrong ! Because rain too much or too little affected the physical and economical lives of primitive people more than it affects ours. So the intellectuals among the ancient did try to explain these natural phenomena.

Greek Gods and goddesses
The explanation put forward by the Greeks was of the supernatural in the form of gods. These gods worked just like the government where Zeus was the chief god (like the prime minister) and he was assisted by other smaller gods which were more specialized in certain fields like:
Athena - the goddess of wisdom and justics
Apollon - God of education, healing and music
Demeter - God of agriculture, grain and bread
Ares - God of war and battles etc ( for more info on greek gods check this site: click here )
The Greeks believed that the tensions and conflicts between smaller gods caused the changes in natures activity on earth. Thus excessive or insufficient rain was the decision taken by gods.

Ceremonies and rituals
People thought that drought and less rain meant that the gods were angry so rituals were made to please the gods. The nature of the ceremony or ritual depended upon the type of effect the people wanted, fore example:
Imagine we are greeks living in 5000 yrs ago and our gods occasionally relax and have fun and parties ! now if at a party a glass of water or wine is broken or spilled it causes rain to fall down from the heavens. So if we want less rain then what type of ritual would we develop ? May be we say that people party less in hot weather so the rite would have people lighting fires and indulging in energetic dances so that all this produce heat which would cause the gods to stop partying !

Conclusion
Two important functions were performed by these mytholgies:

1. They provided supernatural explanation of the natural phenomena
2. They reccomended rites and ceremonies by which humans could interfer with nature's decisions and overcome natural disasters