The fork on the 700 series and Cafe Crusier has a preload adjustment, as well as a compression lockout. Its good to understand both so you can tune the fork per your riding style!
A fork has a stanchion top lever to lock out the fork, which stops the travel of the stanchions completely. Once locked out it performs as a rigid fork which is more efficient as no power you put in at the pedals is lost as the suspension moves up and down.
The compression lockout is the dial on the top right of the fork crown.
When engaged, the compression lockout decreases the low speed compression rate of the front fork, adjustable to the point of being fully rigid.
Turn the preload adjust knob clockwise to increase the spring preload and turn it counter-clockwise to reduce it.
It's simply the initial compression of the internal spring in the fork. The more it's compressed, the stiffer the fork will feel. Bigger preload compresses the spring more, and so it's best for heavier riders and/or people who need/prefer the stiffer ride. Lighter riders should use less preload. The preload adjustment is is one click at a time.