Sometimes a boil on the back is really an inflamed cyst. Cysts can occur anywhere: they're round balls with a firm capsule and stuff inside which looks like pus but really isn't. You can't get the stuff out by squeezing, thoughn trying to do that may make the spot a little sore. Nobody knows what causes cysts. They're only worth removing if they're large enough to bother people. If they are, the way to do it is to get them cut out and stitched by a surgeon. This always leaves a scar, so it's worth checking to see what a surgon thinks a scar might look like, to help you decide.
Most health insurances will cover cyst removal, if the cyst has gorwn in size, causes some pain, etc.