C# is a language designed by Microsoft for the .Net framework. Its syntax is similar to C and C++, with an emphasis on being programmer friendly. It has memory management where C and C++ require the programmer to do this manually, it has array bounds checking where C and C++ don't, among many other differences. Automatic memory management and some other programmer-friendly features of C# sacrifice some performance, but these features can also make development faster and easier. This can be very attractive to businesses and single programmers alike.
C is a rather low-level language, meaning that the programmer sees and deals more directly with a computer's hardware. An experienced programmer can make very efficient and small applications in C that might not be possible in higher-level languages. C is also used to program operating systems and embedded devices where many other languages are not.
C++ is an object oriented offshoot of C, with some friendlier features than C. It is a higher level language, and is certainly more programmer friendly than C. It isn't as friendly or as high level as C#. It is a very common and standard language for general application development.
C and C++ were not designed by and are not related to Microsoft, although Visual Studio will work with both. (Visual Studio also does C# and Visual Basic)
Java is even higher level than C#, and is an interpreted language. It's a rather programmer-friendly language for general application development.
Visual Basic has an English-like syntax, which can be very easy to pick up. It is very programmer friendly.
PHP is a very easy to use (and easy to develop bad habits with) web language.
I suggest choosing one language to start off in. I personally don't think it matters which one. Some suggest learning higher level languages because it's easier, some suggest lower level languages because they'll teach you about a computer.
