A root canal
is a layman's term for something dentists
and physicians refer to as endodontic therapy, in which the living pulp inside of a tooth and the tooth roots is removed, the space irrigated, and the area filled with an inert filler material. Root canals are performed when a tooth has become so decayed or infected that it cannot be saved simply with a normal cavity filling
operation. The root canal procedure allows for any areas of infection and pus down in the root to be washed out and permanently closed over.
Unfortunately there are no obvious ways for you, at home, to determine whether or not you need a root canal procedure. Of course, there are signs that a tooth is in bad shape, such as a large or obvious cavity or a significant amount of tooth pain. However, on the dentist can examine the tooth closely and tell you whether or not you need a root canal.
I highly recommend that you make an appointment with your dentist as soon as possible. The longer you wait, the more likely that the tooth damage or tooth infection you have will worsen, which will only make the need for a root canal more likely.