We use it as adjective to identify something is identical to an other OR is is being use in an expressive manner to put emphasis on something.

The best trick I can give you the recognize it is when, même, is not used as a comparative, it often being use like that : ...même qu'il a dit ça. ... lui-même.

It being use almost the same as even in english. For example

>Oh!, I can't beleive it !! even him did that ?

>Oh, Je peux y croire!! Même lui a fait ça ?

Or sometimes it will be use like you would say himself 

>This as been written by Mi4_Slayer himself. 

>Ceci a été écrit par Mi4_Slayer lui-même. 


Even the French is my native language, I am no expert in the very depth of it's grammar, but I hope this help you to understand more of it use in a sentence.

Also I am from Quebec and we tend to multipurpose more the word même more than our cousins from Europe. But I think it will be enough to get the general idea.