When you buy a pair of skates, chances are that the frame is a flat setup:
This means that all the wheels on the frame are in a straight line and touching the ground at the same time. Since you’re skating on all the wheels, this setup provides good balance, speed stability, but limited maneuverability.
For a rockered setup, the traditional banana rocker is the most common:
The front and back wheels are higher than the middle two wheels with a 2mm rocker between both the 1st and 2nd wheels and the 3rd and 4th wheels. It literally looks like a banana shape, hence its name. This is usually accomplished by either using small wheels in the front and back (eg. 76mm-80mm-80m-76mm), or by having a frame pre-configured with this rocker. It mimics an ice skate blade, and is mainly used for slalom skating. Since you’re only on 2 wheels at a time (with a large 2mm rocker in both the front and back wheels), this setup is extremely maneuverable, but very unstable higher speeds.