Assuming you have two trains running, you'll want to install signals that allow one train to pass while the one behind is held by a signal. Your best bet is to do a trial an error. Install one signal and run the trains in AI. To do AI, you need to add a track mark (red ones) let's say at a station (A). Add another one at the far end of the oval (B). Issue the first command to one of the trains as this: "drive via track mark B" followed by "drive to trackmark A". This train will start at the station and run to (or via) B and continue to A. But if you have another train anywhere on the oval, obviously the first will not run, so now you add a signal somewhere and see what happens. For all this you should also issue the same commands to the second train so both will try to run. Add as many signals as you think train control will be more effective. As per the siding, is easy, just put one signal before the points on the siding, so it will control a train trying to join the "main line".
