When you go in for a tune-up, they basically give you a few (2, sometimes 3) IV antibiotics, combined with at least 3x/day physical therapy and other tests (x-rays, PFTs, etc.) The course of IVs is usually at least 2 weeks, sometimes more. This doesn't mean you are in the hospital for two weeks; if you are at a doctor who permits home IVs, you may get a Piccline placed the second day and be at home for the rest of the course, once you are stablized. Much better deal, if you ask me. But anyway, usually a tune up's called for when you feel especially run down and oral antibiotics aren't doing much. The age tune ups can start varies greatly. I had my first at 5, but I've heard of people who haven't had one until their college years. I'd imagine it has a correlation with when you begin to culture pseudomonas regularly, but I'm not positive.
As hard as tune-ups are the first couple of times, they do get more bearable with time. My biggest tip for the hospital is ASSERT yourself. If a person cannot get an IV started for your child, demand someone else try. There's no need to stick your child over and over again. When you're in there, you may think "Oh they're the hospital, they must know what they're doing." But don't be afraid to ask tons of questions and demand change when things are not right.