Tacking is changing direction by turning into the wind. The following tack is the one taught by ABK clinics.
Begin your turn on a reach (A in the figure below). Before starting to tack,
drop your front hand to the mast just below the boom and move your front foot
to just in front of the mast.
Now begin to turn into the wind by moving the sail to the back of the board
and across the board, just as in the "Steering" section of this guide. You actually will
push the board around with your rear foot as you pull the rig with your rear
hand. As the board moves into the "No Sail" area, swing your body (i.e., butt)
in front of the mast. Keep moving your feet in small steps (1 inch) throughout the turn. If you don't move your feet from the beginning of the turn, you will find it difficult to move them at all.

Keep turning, keeping power in the sail, and keep swinging the sail over the
board well past the "eye of the wind" until Position B in the
figure. You should be well past the "No Sail area" before changing position
on the board.
When you are in Position B, change from one side of the sail to the
other in the following manner. First, move your back foot next to your front
foot (in front of the mast) and move both hands to the mast. Second, move your
old front foot back on the other side of the mast and your hands back to the
boom on the new side.
Finally, you will probably want or need to turn further off the wind, so
aggressively move the sail forward and across the board (just as in the
"Steering" section).

It is helpful to keep your arms straight while tacking. Also, remember to keep
your knees bent.
The important principle in the tack described above is that you keep power in
the sail for as much of the turn as possible. While there is power in the
sail, you probably will not fall. However, if you change from one side of the
board to the other at point "c" in the figure ("No Sail Area"), you will be
standing on the front of the board with the sail "flapping in the breeze" (no
power in the sail). You will be "wave bait" (the first wave will probably
bounce you off your board). The sailor is seen standing helpless, praying that
some mysterious power will finish the turn. This tack is called the "rope
tack" and the sailor resembles a cowboy holding on the to the reins (uphaul)
while riding a bucking bronco. The rope tack works fine in a smooth lake, but
not where there are any waves.
Fast tack
It is interesting to watch racers tack. One moment they are on one tack, and in the blink of an eye they are on the other tack. The tack described above will be slow and deliberate. One thing that you can do to speed the tack is before beginning, when you move your front foot just before the mast, also move your back foot a few inches back on the board (so that you have a wider stance). Having a wider stance will give your back foot a bit more pushing power.
When racers tack, they literally jump from one side of the mast to the other, cutting to a split second the time they are in front of the mast. Two factors allow them to move so quickly. First, they may change position while "head to wind" (Position c). However, then they aggressively throw there rig forward and across the board so that they head downwind on the new tack. Like its slower cousin tack that I recommend above, there is power in the sail for nearly the entire turn. Second, racers are going very fast going into the turn and their momentum helps them complete the turn. As you get better, you will realize that in all things, speed is your friend. There are many things that you can "pull off" when you are going fast that you can not do when going slow. Always sail as fast as you can.
AAA on the water - Jury rig
What if something breaks and there is no one around to help? It is usually possible to jury-rig your board and get home. Many sailors carry a 6 to 10 foot rope (1/8 to 1/4 inch) to help them out of several different kinds of jams.
If the downhaul, outhaul, or uphaul breaks, no problem if you brought that piece of rope with you.
If your boom breaks, all is not lost. Usually the boom will break on one side, near the mast. If the broken side is not the side you need to hold as you sail home, you have no problem. Simply lash up the broken piece of boom so that it does not poke a hole in the sail and gently sail home. You only really need one side of the boom anyway. If the broken side is the side you need to hold on to (windward side) you can do one of two things. First, you can take off your boom, turn it over, and rig the sail again. Now the good side of the boom is in the correct place. Your second option, if you don't have far to go, is to sail "clew-first" (see 'Free style' in 'Where to go from here').
If you hit an obstacle and lose your fin, the back of the board will want to swing around. You have to rig some kind of "sea anchor," a drag attached to the back of the board, to keep the back of board from swinging around. Attach something, like your harness, wetsuit jacket, etc., to the back of the board and let it drag in the water. If you have footstraps on your board, attach something (your harness) to them.
If the mast breaks above the boom, you can usually sail home with part of a sail. If the mast breaks below the boom, you have a worse problem. You will have to figure out a way to lash the bottom of the broken mast to your board.
If you picked your sailing site carefully, you will not be sailing in an off shore wind. Because you are not sailing in an off shore wind, you will not have to sail against the wind with your jury-rig.