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.
english.stackexchange.com/users/31/Brendan Berg
I use yeah or yep
/yup when speaking casually.
I tend to use yep/
yup when it is being spoken by itself.
I also would correspondingly use nope in the same way.
Did you do it?
Yeah, I did it Yep.
english.stackexchange.com/users/380/Mr. Shiny and New 安宇
Yes is not a formal word; you can use it in both formal and informal contexts.
Looking at the definitions given for
yeah , yeh , yep , or yup , all those words are defined as exclamation & noun nonstandard spelling of yes, representing informal pronunciation.
Looking at the examples provided from the Werriam-Webster Online , it seems that yeah , and yep are used in two different cases.
Yep is used when it's the only word in the answer; yeah is used in the other cases.
That's really what she said?
Yep.
That looks good.
Yeah, I think so too.
english.stackexchange.com/users/252/kiamlaluno
Yeah can also be used in a partial negation [yeah, but] meaning that you are affirming only a portion of the question.
Friend: Did you get movie tickets for me with the money I gave you?
You:
Yeah, but they cost ten dollars more than you gave me for them.
Would you be willing to pay for the popcorn?
Friend:
Yep.
You:
OK.
See you there.
english.stackexchange.com/users/3328/Zoot
In spoken (and informal written)
English, I generally use yeah or yup .
I mostly use yes when additional emphasis is needed, possibly with additional words as confirmation, e.g. if someone said I hadn't completed a task, I might reply
Yes, I did.
In formal written English, Yes should be used.
You might see this, for example, on application forms which have Yes/No tick boxes or similar.
english.stackexchange.com/users/303/Steve Melnikoff
Usually people write yes, unless it is informal writing, then
yeah
and yep can be used.
In spoken English yes is always appropriate, but with friends and relations
yeah
and yep are frequently used.
Sometimes the words can carry more meaning by their tone and repetition.
Mother: "Did you you do your homework yet?"Child:
"yeah,
yeah,
yeah.
" (The homework not done, but the child is tired of being told about it.)
english.stackexchange.com/users/914/Picturepocket
When agreeing with someone I prefer "yeh" whereas with an exclamation such as "yeah, he scored the winning goal"
the "yeah" is cognitively quicker to come off the mind than discerning first whether you want to spell it "yeh" or
"yeah" knowing that the latter has more than one meaning.
english.stackexchange.com/users/None/
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?
When is it appropriate to use "Yeah" and "Yep" as variants of the word "Yes"?
english.stackexchange.com
<synonyms><conversation>
english.stackexchange.com/questions/1954
english.stackexchange.com/users/142/rem
"Yeah" and "Yep" are informal variants of "Yes", although "Yep" has a slightly dismissive tone. In a conversation among friends, any form is appropriate. "Yeah" can be used in a partial negation where you are affirming only a portion of the question. In conversation among friends, any form is appropriate, but "yep" has a slightly dismissive tone. Other variations between the terms will depend on context.
"Yeah" and "Yep" are informal variants of "Yes", although "Yep" has a slightly dismissive tone. In a conversation among friends, any form is appropriate. "Yeah" can be used in a partial negation where you are affirming only a portion of the question. "Yeah" and "yep" are informal variants of "yes." Yes  also gives more emphasis. In formal written English,  Yes  should be used.
"Yeah" and "yep" are indeed informal variants of "yes." In conversation among friends, any form is appropriate, but "yep" has a slightly dismissive tone. In general, in informal situations, "Yes", "Yeah", and "Yep" are all perfectly acceptable. "Yeah" may imply that there is more information to follow, whilst "Yep" is used more in one-word answers and can be perceived as a little dismissive.
In conversation among friends, any form is appropriate, but "yep" has a slightly dismissive tone.  Yes is not a formal word; you can use it in both formal and informal contexts.  Yeah can also be used in a partial negation [yeah, but] meaning that you are affirming only a portion of the question. 
"Yeah" and "yep" are informal variants of "yes." Yes  also gives more emphasis.  In formal written English,  Yes  should be used.
Yes, Yeah and Yep are all acceptable in informal situations but only Yes is acceptable in formal situations. "Yep" is generally used for one-word answers and can be perceived as somewhat dismissive. Use of "Yeah" may imply that there is more information to follow.