What is l operator used for?

Answer 1

| is the bitwise OR.

Example:
#include <iostream>
#include <bitset>
using namespace std;

int main() {
cout << bitset<8>(0b10101010|0b00001111); //output: 10101111
return 0;
}

Other bitwise operators: & (AND), ^ (XOR), ~ (NOT), << (shift left), >> (shift right).

Answer 2

This is not covered in this course. Bitwise or is like the || logical or you learned here, but it is used on binary numbers, that consist of only 0 and 1 :
0 | 0 = 0
0 | 1 = 1
1 | 0 = 1
1 | 1 = 1

If we use this operator on two binary numbers, the first position of the first number is or'ed with the first position of the second number, the second with the second and so forth

ex

0011 | 0101 =

0011 |
0101
------
0111