Once you are confidently catching green waves you naturally want to ride them for as long as you can.
Trimming along the wave face is not really considered a surfing manoeuvre but it is an exciting feeling that leads you to the sensation of doing turns.
Trimming is subtle up and down movements that keeps your board in the fastest part of the wave. It maintains your flow and allows you to ride a wave for as long as possible. Without trimming you may loose speed and fall off. Small up and down movements with your knees changes your centre of gravity. It is a natural response that you will find yourself doing.