Tacking means turning towards the wind. Sailing at beam reach, start luffing so the board steers windwards until it gets into the wind. Then, place your feet at the nose part of the mast and change the sail from side to side above the tail so the board finishes steering. To make it easier, you can use the boom. Finally, change your position and bear away slightly to start at the new course.
The first step for tacking is LUFFING, the second step is going to the other side of the board following the mast foot, and the last step, once you are on the other side of the board, is bearing away.
According to the picture on the right, during the first step, your right hand (front hand) must be placed on the mast and your back hand on the boom. When going to the opposite side, at the last step, your hands must change positions, your left hand (front hand now) being on the mast and your right on the boom.