Pops one string that represents the name of the function to call, pop one integer indicating the number of arguments following, pop each argument, call the named function, push the result of the function on the stack. There is always a result1.
The concept of a function in SWF is the same as in most languages. The function uses its own stack and local variables and returns one result as expected. However, be careful because functions declared in a movie before version 7 could stack multiple results and they all were returned!