Free-Float Release Lever
The free-float release lever allows you to lock the chair from reclining at any tilt position, or to let it rock freely. If your chair has this function you will have a lever on one side of the chair. Usually it is located where you can reach it comfortably while sitting in the chair. Push it up or down to free the chair to rock or lock it at any intermittent position.
Tension Adjustment Knob
Setting the tension of the chair so you do not lean too far back too fast is very important. It also makes the chair more adapted to your body and personal preferences. The tension adjustment is typically made by turning a large knob under the front seat of the chair. Sometimes the tension control is a small crank and not a knob. In either case, turn it clockwise or counterclockwise to set the spring for the amount of resistance you want for your chair tilt. Make sure you have enough tension so your back is supported and you don't fall backward when leaning back, but don't set the tension so high you have to force the chair to recline using your hands or feet.