I have a Bachmann 2 wire N scale set up and would like to add a siding to park one loco while using another.
Hi Donon,
You can either block (gap) the siding using an insulated rail joiner and an on/off switch, or use a power routing turnout to the siding.
Look here, scroll down to basic wiring there is a simple picture;
http://www.nmra.org/beginner/wiring.html
Good luck