1. Affirmative, yes, to convey agreeance.
2. Gives the subject a good characteristic, feeling or appearance.
Example: In the case of (2) this is a contextual word, ie: the use of the words around it define the exact meaning of yep.
Examples:
"She is all yep" - The subject is in some way desirable, or has said or performed something desirable or agreeable to the speaker.
"Yep, that's a yep" - A double confirmation. Generally used after confirmation has been asked for on a particular subject.
The word you use when you really want piss your girlfriend(s) off after they send you one of those messages where she is trying to spark a long in depth conversation about your relationship after you simply say "i am going out tonight."
That response to a question that is both legitimate and sarcastic; as in Storage Wars..."Yep" Said in a sing-song way that confuses all those listening
Example: Dude, you joining us for some beers after work? Yep
Hey, did you get that report done for the meeting? Yep
Example: Usage is similar to that of the Golfer's "fore". After having thrown say, a steel ball bearing the size of a grape at your workmate across the factory floor, it is a courtesy to give a loud and clear "YEP!" before they are hit.