most of your questions are answered in the stickies. But being a nice guy, you can buy coolant/antifreeze from your local auto stores like pep boys, autozone, kragen, etc. When water gets low and you only need to add a little, then you can just add distilled water. If you want to make sure, just add a solution of mixture of antifreeze to distilled water. Most people like 10-15% of antifreeze to water.
Anyway, read the stickies. I certainly did when I first started out.