Function

How can i create a function on arduino?
Can you post an example her please.

void setup()
   {
   //  This is a function
  }

void loop()
  {
  // This is also a function
  }

int AddFive(int argument)
     {
    // This is a function that takes an integer argument and returns an integer value
    return argument + 5;
    }

how can i return to the loop in the function.
And what i put in void setup to create an function

If you spent some time on the tutorial section you learn quite a lot about how the Arduino programming Language works.

also the reference pages are very instructive to get started , you will learn what the Arduino can do (there is plenty more )

e.g. more about loop - http://arduino.cc/en/Reference/Loop -

how can i call an function?
For example i´m in a function and i want to go to the loop. what is the command (return loop)?

It is all in the reference pages I mentioned before, please read them,