You buy tap water conditioner at the pet store. It says it right on the bottle. Follow all the directions carefully.
All fish require filtration, an air pump and a heater. Please, please, please Google it. There are hundreds of sites to get you started right with aquariums. Each fish will have it's own needs. Just like you wouldn't put a dog in a bird cage...you have to handle each fish properly.
It's a myth that a betta can live in a vase with no heat or filter. They can't. No more than you can live in your closet all day, eating, pooping...no. They don't need an air pump, but that's only because they have a special organ in their gills, and even then, they do better when they have one. ALL other fish need air pumps.
There are books you can read. I know...read a book?!? LOL!
Libraries have them for free. Ask the nice ladies at the desk, they'll show you where to find them.