The basic process is first getting your pet which does not only need to be a dog used to the click sound then a treat. This is repeated a few times, which will associate the click as reward time. Some people use pointers to help with the training, you can buy a clicker which has a built in pointer or you can use a pencil or straw. Once your pet knows a click means reward you can start training many other tricks very easily.
The point of the clicker is just to show the exact gesture he is currently doing is correct, so either click then reward just as he sits. Repeat this without any cue and then once he masters that, put in the cue during the gesture while still using the click and treat. Then the last step is to give a cue then he does the trick, which is followed by a click and treat.
This is a great way to train your pet without having to resort to any sort of punishment. Punishment actually hurts the process of training since it is usually punished after the act has been done and does not associate the two together.