Root Canal commonly called as RCT is the process by which the canal of the tooth is cleaned till its root before putting some filling inside it!
The teeth is drilled, cleaned and canal ( proper shape) is prepared.
Yes an injection of anaesthesia( to make the gum numb) is given when tooth is being drilled so as to avoid pain in nerves.
RCT is done when tooth is in bad shape,(Broken, infected)
After the injection is given, there is no pain. and RCT process generally involves more than one sittings