Selecting [Enable] lets you use the multi selector to choose the starting focus point when AF-C and [Auto-area AF] are selected respectively for AF mode and AF-area mode. The camera will revert to normal auto-area AF once you have focused on the subject in the selected focus point.

A Custom Settings: Fine-Tuning Camera Settings

a: Autofocus

b: Metering/Exposure

c: Timers/AE Lock

d: Shootin/Display

e: Bracketing/Flash

f: Controls

g: Movie