Re: Overheating/coolant issue
Sounds to me like your heat exchanger is toasted - leaking into the raw water side.
It works by holding the water/anti freeze mix in a tank, and the raw water is pumped through it via a bunch of little tubes. If one or more of those tubes is corroded through it's shot.
To replace it isn't that hard, but if you truly have no experience it might be better to pony up the bucks and have a mechanic do it, and while he's there also check the rest of the engine.
Lessons learned are opportunities earned.