C is the original language because some programmer was boring as fuck and decided to name a language literally just the letter 'c'.
C++ is from some guy that made it better, and it's a joke because a ++ after an integer variable name means that you're increasing the variable by 1. So it's basically saying that it's 1 better than C. It's shitty nerd humor, okay?
C# is another dumb pun because the # means sharp which is one semitone higher in pitch. I guess this guy was making fun of the guy who named C++.
And that's your short guide to the C's. I think there are other derivatives but those three are the ones people still care about.
If you want more stupidly named programming languages, look up what PHP stands for.