Setting is an action that allows another players on your team to get a good hit towards them to spike the ball onto the other side of the court. Setting is done softly with your fingertips, not with your palms.
Bumping is an action that allows your team to gain control of the ball to set and spike the ball onto the opponent's side of the court. This is done when you straighten your arms and fold your hands together. You have to make sure that you don't lock your fingers.
Spiking is when you hit the ball as hard as you can at the ground on the other side of the court with your palm. Usually other teammates help set you up for a spike.