What happens in assembly language when you call a method/function?

If I have a program in C++/C that (language doesn't matter much, just needed to illustrate a concept):

#include <iostream>    

void foo() {
    printf("in foo");
}

int main() {
    foo();
    return 0;
}

What happens in the assembly? I'm not actually looking for assembly code as I haven't gotten that far in it yet, but what's the basic principle?