A root canal is needed with an infection gets deep enough into a tooth that it causes damage to the root. In order to remove the infection, essentially the entire tooth has to be drilled out and reconstructed at this point. This is a "root canal."
There can be some pain and bleeding
associated with the procedure, however these are usually quite minimal and managed by anesthetic medicine injected at the time of the procedure.
On the other had the complications of not having a root canal could be very severe. In addition to the ongoing pain from the erosion of the infected tooth which you are probably dealing with everyday, there is also the risk that the infection will worsen and get into the blood stream, potentially spreading to other parts of the body and causing major problems.
Therefore, I highly recommend that you follow your dentist's advice on this one and set up an appointment to have your root canal performed as soon as possible.