There should be a series of buttons on the top front of the refer. Off/on, Gas/elect/auto, and temp set. Turn it on, press the button to electric, set temp to three, close the door and go inside and forget it for 24 hours. After about two hours you should feel the floor of the freezer getting cold.
OOPS that is for a RM2852.
BTW the slider thing you refer to is the adjustment and should never need adjusting. One way makes the box warmer, the other way colder.
The refer needs 12VDC and 120VAC or Gas to start and run. 12VDC for the control circuit, and then gas or 120VAC for the heater to cool the unit.