Lark has already given the first reference I would recommend. That is a great source for information on the Greek deities.
I have been a follower of the Greek gods for just under 30 years, so I have accumulated a bit of knowledge. I would be more than happy to share what I know, but I would need to know more about you. Are you over 18? I am legally ordained clergy, and have to be careful, as it is illegal to give religious instruction to a minor without parental consent. Many states have this law, including the one in which I live.
The Percy Jackson novels are fun reads, but are not tools for learning Greek mythology. Many of the concepts in the novels are not at all in line with the myths. Read those books for entertainment and gun stories, but not for actual information about the gods and goddesses of Olympus.
Seriously, Percy Jackson teaching youngsters about Hellenismos? I doubt it. It gives a basis for the mythology, but that is it.
Here are some sites that might help you out:
http://www.theoi.com/ (As already posted)