Your park admission covers the Monorail. The line only has two stations: Tomorrowland and Downtown Disney (formerly Disneyland Hotel Station). You can get off at Downtown Disney, but you must get off at Tomorrowland. Unlike Florida and Tokyo, Disneyland's Monorail is a second entrance for Disneyland (you can leave the park on it and it can bring you back). Cool, huh?
Everybody hit the nail on the head, You can use the monorail freely as many times as you please as long as you have park admission, but everybody has to exit in Tomorrowland, I was in the park today and the wait to enter the monorail in Tomorrowland was all the way to their entrance, it was about a 45 - 50 minute wait, insane.