Surfboard wax is applied to the deck of your board to create a textured, grippy surface.
There are no hard or fast rules of how to do this, simply rubbing it on will do a good job as long as it covers the area where your feet and hands will be, though if you want more specific instruction below is a little guide that will get you started if it's your first time.
Before you begin make sure your board is clean and free of dirt. Start applying wax with flat side of bar down in a tight circular motion (about 15-20cm) while pressing firmly. As wax starts to build up, move along the board. If you continue in a small area, the fricton will flatten the bumps rather than build them, so try to maintain constant motion lengthwise along the board.
Once your board has a nice set of bumps, turn the bar vertically and do long parallel strokes down the length of the board, this really builds up the bumps, increasing the grippiness of your board.
Wax the complete board including nose and tail areas. Even if you aren't at the level where you're riding the board from the tip or tail, waxing then will help you with retrieving your board in the surf. Wax to the edge of the board, but not onto the rail or else they will tend to grab your legs during transitions from sitting to paddling.
If you have a brand new board and want to apply a base coat, though this is not strictly necessary simply use a warmer wax than is needed for the water temperature that you will be surfing in, this will lay down a nice hard coat of wax to which you can then apply a softer wax on top. This will keep the wax being completely wiped off the board in warmer waters. For example warm water wax is quite hard, cold water wax is soft.
