It's not a dumb question.

The blue/red wheel is the temperature wheel. Depending on which CCU you have installed, it'll be marked in Centigrade or Fahrenheit. Blue is A/C, white is mixed, red is heat.

Fan switch is Max or Min fan speed. Pressing "Automatic" will allow the CCU to vary the fan speed automatically depending on setpoint and current cabin temp.

Mode buttons left to right: Defrost, Defrost/Floor, Automatic, Economy, Off.

Defrost defaults to max fan/heat at the defrost nozzle at the windshield. Defrost/Floor will run in automatic mode to maintain temperature using defrost and floor vents. Automatic will vary the vents in use depending on temperature in the cabin, temperature outside, and the desired setpoint. Economy is the same as Automatic, but disables the A/C compressor. Off is just that - Off.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]