Root canal treatment (also called endodontics) is needed when the blood or nerve supply of the tooth (called the pulp) is infected through decay or injury. The nerve of the tooth becomes inflamed which can lead to extreme pain.
Your dentist will numb the tooth using local anesthetic, then remove the inflamed nerve and clean away the infection. Once this is complete the tooth will be filled with a rubber like material, then restored with a filling.
Having a root canal treatment should feel no different than any other ordinary filling.