First of all NEVER AND LET ME SAY AGAIN, NEVER USE WD-40 ON ANY KIND OF METAL, NOT EVEN ALUMINUM...EVER!
WD-40 causes rust on metal!!!
Keep your bike dry and out of humidity...PERIOD.
The only way to inhibit rust on your chain is to keep it oiled with the proper bike chain lubricant (and all pivot points and anywhere metal touches metal)
If you have a bike that is rusting then I would recommend that you get rid of it (when practical) or take it inside but since it has started to rust ...you cant stop it now that it has started. Get an aluminum bike frame and spend a bit more to get quality rather than the dept store bike you obviously have...That will really stop the rust! I cant think of any diagrams to show you how to stop the rust, this is common sense stuff that you are going to have to experiment with and get the bike out and away from moisture - even when its cold outside there is still humidity in the air and that will cause rust. If you cover the bike with a plastic sheet that will trap moisture underneath and cause rust. You have a bike w/ metal parts, sorry but not a whole lot you can do once it starts.
Just spray ur bike all over the chrome and metal parts with a light coat of WD-40. go heavier on the heavy rusted spots. wipe excess with rag and make sure the WD-40 won't interfere with ur braking system. Don't spray the rubber brake pads or the wheels rim.