why we use "endl" in double making program

Answer 1

To move next "command output" for example cout output to the next line:
lets say we want to have output like that:
-Whats up?
- Nothing.
So u have to move nothing to the 2nd line to make it looks like conversation. thats why after "cout << "-Whats up?" u have to add " << endl;"

Answer 2

endl means EndLine. Like when you press Enter on your keyboard

Answer 3

endl used so that the output will not be print in a single line