How to have a horizontal slider on pygame screen?

[Pythonslayer]

I have just begun learning pygame and am trying to code a horizontal slider that changes the speed of the game but don't know how. I found this website https://pygame-gui.readthedocs.io/en/latest/theme_reference/theme_horizontal_slider.html and it seems as if it has an in-built function or so but I don't know how to use it (I don't understand what I need to do to implement it and how).