LibGdx Screens and stages

What are the main differences and how to i use them. I´m following a tutorial that uses screens as the base. Now i would like to add Touchpad to the screen, but it requires stage.

Do i need to recode the game into using stages as base? If yes, can someone give me a tutorial that does that, so far i have only found game tutorials that extends Game and uses screens.

Is there a way to combine stages and screens, so that i don´t have to rewrite the game, instead i just add stage to the screen and add Touchpad to the stage then. If yes, then what would be the way to go to do this?