Explosiveness and Quickness
Quickness allows a player to make a variety of moves: cutting quickly to the basket, playing smothering defense, finishing at (or above!) the rim, or pulling up for a shot.
Quickness requires two key inputs. The first input is strength - how much weight your muscles can move. The second input is speed - how quickly your muscles can move weight. Neither a bodybuilder nor a marathon runner have great quickness: one has a lot of strength, but little speed; the other has a lot of speed but little strength.
Weights develop strength in your lower body and core. Start with squats, leg press, lunges, planks, and dead lifts. MAKE SURE you are using good form, and consult a physician and a trainer before starting a weight training program.
Plyometric exercises to develop your speed. Depth jumps, lateral box jumps, and agility ladders are a great place to start. Make sure you consult a doctor and a trainer!