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Just like it says.
First step in on switch is on. Push and release for resume or accelerate (RA).
Button on the end is for set speed. It also does coast (sets a slower speed) buy holding it in. When you release it at the lower speed it will hold it there.
Generally, one push of accelerate equals about 2 mph increase. So 2 pushes is 4 mph, 3 is 6 mph, etc. Holding it will accelerate until you let it go.
Cruise is canceled by turning it off, hitting the brake switch.
Turning the truck off or turning cruise off wiper the speed setting and resume will not bring it back to the previously set speed.
The brake switch just cancels cruise and pressing resume will bring it back to the last speed setting.
Owners manual tells you all this. You should read it or get one if yours is missing.