First depending on your symptoms, your endodontist may run some simple tests to help determine a diagnosis.  If the diagnosis is that you need root canal treatment, you will either be treated at that time or appointed for treatment.  This is usually determined by your current symptoms (are you in pain!).  If treatment is needed it will involve local anesthesia (like what you would get to have a tooth filled), isolation of the problematic tooth with a rubber window (latex or non-latex dental dam), and may require one or two visits to complete depending on the anatomy of your tooth and severity of the problem.