Are you asking what to do if you can't have a quarantine and are buying new fish, or do you have fish that are sick and want to know how to treat them without a quarantine?
Most people use very simple setups for their quarantine tanks. The tank is usually small, 20-40 gallons and some people use Rubbermade tubs, with a heater, powerhead, and either a sponge filter or a HOB filter. Lights are optional as long as there is some ambient light in the room during the day. Some sort of cover (bird netting over a frame works well) that still allows air movement is a good idea.