From the left:

Button 1: Defrost: Blower at high speed, temperature at maximum, defrost vents open. a/c compressor engaged.

Button 2: Blower runs in stages 3-5. In heating mode, air goes to defrost vents, side vents and legroom vents. In cooling mode air goes to above and also to center vents. a/c compressor engaged.

Button 3: Blower runs in staged 2-5. In heating mode air goes to legroom and side vents. In cooling mode air goes to center vents and side vents. a/c compressor engaged above 4C.

Button 4: Same as button 3 without any a/c compressor.

Button 5: All vents closed. Blower not operating.