Emacs as an IDE

[polymedes]

I would like to use emacs for software development and I currently am
learning it. I use the command "dabbrev-expand" (bound to M-/) to
expand (autocomplete) funtion and variable names. But how can I see
the function definition _while_ I'm typing ?

In all IDEs when you type the opening parenthesis a tooltip shows you
the arguments that you should pass to the function.

What do emacs developers usually do?

Furthermore, if the function is overloaded how can somebody know all
the definitions?

These questions apply to C++, Java, Python and C#