How do you set up at OBS that you can hear other players e.g. In Fortnite?

I have a question and I'm making new videos and the problem is you can't hear the other players in the video just doing yourself?

Did you switch on the "desktop microphone"? And do you hear the tone of the game?

If you hear the sound and also communicate with her on the computer, this should actually work.

My friend about ps 4

But you hear the sound from him on your PC?