to ride the rides, just hit the little red car button once you click on the ride.. then hit the light purple camera button... then it will put you in coaster cam mode, then you can slect differnt angles and different cars to ride in
Also, depending on which version you are using (RCT, RCT2, RCT3) there is a limit to the number of stations you can build. The length of the train also dictates other things. Make sure if you have a long train that each station is long enough to accommodate the trains, or it won't let you open the ride or make the trains as long as you want.
But, in any case, if it is a complete circuit of your Park then after connecting the final piece of track back to station that you started at, you have the add the Entrance and Exit to that station, then go to the next station, click the construction icon and add the entrance/exit then to the nest, and so on until every station has an entrance and an exit
Then you need to open the icon for vehicles and pick the type of monorail you want, and how many passenger cars you want, the colors and so on. Then set how long the Monorails should wait before leaving or if they should leave when a new train comes in, etc.
Then click the maintenance icon and set the inspection to 10 minutes if you want a big layout to run smoothly. Then put a mechanic at each station entrance and fix his area around that station.
Then go back to the main station, open the ride in Test Mode and watch it run. If you have four monorails make each one a different color, and watch each and every train go around the Park to make sure they complete the circuit without running into the rear end of the train in front, etc. If everything is set, build your paths and queue line to the entrance and exits, put a No Entry sign at the exit path so the peeps don't go up there and have to turn around and go back to find the entrance, that will give the ride bad word of mouth. Open the ride then in normal ride mode. And you can watch or ride.