Sharp turns that redirect the board quickly on the face. The move behind most of what you see in a competition.
A carve is a long, drawn-out turn that uses the rail. A snap is a quick, tight turn on the lip that throws the tail out. Both use the same mechanics: speed, a clear target, and a body that leads.
Speed first. Build it with the bottom turn and a high line.
Look at the target on the lip.
Rotate the shoulders and hips together in one move.
Throw the tail out by pushing the back foot, keeping the front foot on the rail.
Recover: bring the board back under you, with your eyes on the next section.
Mistakes
Snapping from slow speed. It stalls and you fall behind the wave.
Throwing only the legs. The shoulders and head start the movement.
Not finishing: a snap that ends with your weight behind the board loses all speed.
A guide is not a coach. If you can, take a lesson or surf with someone better than you.