A port is a device that is placed underneath the skin (most that I have seen are in the chest in the collarbone area). It feels kind of like a drum under the skin. The way to access it if you are needing to flush it or give medications through it is a needle is placed through the skin into the middle of the "drum". I don't have one, so I can say from personal experience, but I have been told that it isn't very painful, and some people really prefer it to PICC lines. It does require a surgery to put it in, but it can stay in for years as long as it is viable and, as I understand, only needs to be flushed once a month when it is not being used for medications. As far as when to start it, my doctor has said that when I start needing IV meds more often, like 2-3 times per year, I might get one. But as you probably know, every case is different, as is every doctor.
I hope this has answered some of your questions.
Marisa RN, 21 w/CF