Root canal treatment is done when there is no chance of tooth to be saved, and the patient doesn’t want it to be extracted although decayed. It is done to kill the vitality of the tooth and then filling it with mechanical components, and placing a cap over it.
The procedure involves the removal of the nervous elements of the tooth which have been infected or decayed already due to microbial action or any physical pressures.

Here is a video that demonstrates the entire root canal procedure in a simple way(Its an animated video to clearly show how the procedure is done), check it out below -