synonyms - When is it appropriate to use "Yeah" and "Yep" as variants of the word "Yes"?

As a learner of English I know that yes is a standard variant and the other two are informal, spoken words. I know nothing more about it, and always try using the yes variant, just to not sound inappropriate. But I'd like to be able to not sound too formal in a casual conversation.

Could you help me understand the differences between these words and the contexts in which it is okay to use them?

Answer

You are correct that "yeah" and "yep" are informal variants of "yes." In conversation among friends, any form is appropriate, but "yep" has a slightly dismissive tone.

"Did you find your wallet?"

"Yeah, I left it in the other room."

As opposed to

"Did you get directions to the theater?"

"Yep."

In the second example, you're implying that you've already got directions and you don't need to spend time hearing them again.