c++: what does this insertion expression do and how does it work when passing as a function argument?

What's the meaning of binary(number >> 1), and how does it work in the following code? Could somebody explain it to me in detail? Thank you!

#include <iostream.h>

void binary(int);

void main(void) {
    int number = 3;
    cout << number << endl;
    binary(number);
}

void binary(int number) {
    if(number <= 1) {
        cout << number;
        return;
    }
    int remainder = number%2;
    binary(number >> 1);  //How does this work exactly?   
    cout << remainder;
}