Career development encompasses many things. For civilians, it might mean professional reading, obtaining certification in a particular trade or skill area, further training, an advanced degree, or just learning more about the civilian placement, evaluation, and promotion systems.
For military personnel, it can mean different things depending on whether you're enlisted or an officer. For enlistees, career development involves "A" and "C" schools, taking Coast Guard Institute non-resident training with PQGs and tests, getting EPQs signed off, servicewide exams, equipment training, Coast Guard knowledge through the new E-PME system, professional reading, perhaps getting a college degree, and many other things.
Officers develop their careers by performing many different primary and collateral duties, reading professional publications (and, perhaps, writing for them), and pursuing advanced degrees.
The information linked to the menu items on the left is intended to help you with all these.