I really want to know about the environment?

I really want to know all about the environment and how to help it. For example what is the clean air act, the EPA, climate and energy legislation ect. I want to watch the movie The 11th Hour but before that I want to know what I am going to be hearing. I really want to know what kind of work Leonardo Dicaprio is doing for the environment so forth. So if anyone could give me the name of a site, or tell me here all that I need to know to understand ALL that is going on in the environment.