These instructions will help you with completing your solve. For more information on this, see Article A of the WCA regulations.
1. Sitting or standing?
When solving, you may choose to stand or sit. It's mostly a matter of personal preference, so choose which ever is more comfortable to you. If there's not a chair at your station, there might be one immediately behind it, and you can simply pull it up. If there is a chair and you don't want it, push it back. If you want to sit and there is no chair, ask your judge for one.
Before you solve, you get to study the cube for 15 seconds. When you go up to the station, your puzzle will be covered. There will also be a Stackmat timer on the table. Don't touch that yet! The judge will ask you, "Ready?" Respond with "OK" or "Yes" or a nod of the head and the judge will uncover the puzzle. Pick it up and study the puzzle. Don't make any moves on it yet or you'll be disqualified. The judge will call out two things during this inspection. At 8 seconds, they will say "8 seconds". At 12 seconds, they will say "Go". When they say "Go", you will need to start your solve very soon to avoid a penalty. Remember, the timer takes about 1 second to start up, and you will take some time to put down the cube. You must start your solve by 15 seconds, the judge won't tell you anything after "Go" at 12 seconds.
Note: You have 15 seconds of inspection time, but you're not required to use the whole thing. If you're ready to solve after 6 seconds of inspection, then just start your solve.
3. Starting the timer
The timer used in WCA competitions is the Stackmat timer from Speedstacks.com. When starting your solve, place both hands on the timer where the picture of the hands are. When you do this, the red light will turn on. Leave both of your hands on until the green light turns on (about 1 second). Once the green light is on, you can remove your hands to pick up your cube and solve it. The red and green lights will flash while you're doing your solve.
While solving, avoid touching the timer, since doing so would stop it. If you're sitting down, make sure your forearms don't brush against the timer.
4. Solving the cube
Solve the cube. You came to the competition, so obviously you know how to do this, right? Good. If you happen to "pop" your cube, then put it back together and finish the solve. If you get an "unsolvable" case when you get to the end, take the cube apart and fix the problem. When you finish your solve, you want to put down a solved cube, or your result will be a 'Did Not Finish', or DNF. If you get 2 DNF's in a single round (1 for a Mean of 3 event), you will not have an average and probably not proceed to the next round. Even if you have a slow time, always try to put down a solved cube.
5. Stopping the timer
When you've solved your cube, put the cube down and put both hands on the timer. Stop the timer with both hands flat and palms down. Do not do a karate chop, do not use your wrists. If you quickly tap the timer and pick your hands up again, the timer may not stop. Put both hands on there and leave them on until the lights stop flashing.
At this point, do not touch your cube or the timer. The judge is going to make sure that the cube is correctly solved, and then he will record the time from the timer. The judge will write down your time and then have you sign/initial the score sheet. Do not sign unless you agree with what the judge has written.