For each pickup there is a volume, filter control, and off/on/bright switch.
 
At the filter controls, inside the control cavity, the trimpots are for the gain of each pickup. You can adjust the height of the pickup and only worry about it's affect on the tone. Then later you can adjust the trimpots and change the gain without affecting the tone at all.
 
The switches on your guitar are pickup selectors. When you're in playing position from top to bottom it's:  
 
off  
on  
bright  
 
The trimpot inside the control cavity on the switch is the amount of brightness. Turn it clockwise to get a bigger difference between the middle and down positions.