How do I slow down a section in OS?

[michaelmcallister1]

Many creators use this, but I don't know how to do it. (If you don't know what I'm talking about, it's those arrow things at the top of the screen)

[Benvisions]

markers

[oatmealboi]

right click the area where you see the markers, select your item thing you want to change and hit the plus

[michaelmcallister1]

How do I use markers then?