I had surgery for this recently. Here's what happens.
A septoplasty is usually performed when the septum becomes deviated enough to interfere with normal breathing. There's also a chance that polyps can develop because of this condition -- they are rarely dangerous, but can cause irritation if they take up too much of the nasal cavity. Septum deviation is a fairly common affliction, but for most people, it's not extreme enough to become any big problem.
Normally, this is outpatient surgery. It's not, however, wart removal -- you'll have to strip down and wear a surgical gown. You'll have an intravenous line inserted, and you'll be placed under a general anesthetic -- in other words, you'll be knocked out for the operation.
Once the patient is safely in slumberland, the surgeon will use a nasal speculum to open the nostril and spread it wide enough to see and work in. After that, the mucous membrane of the septum will be cut, separated, and raised from the bone. The cartilage of the nose will be cut, and the mucous membrane elevated. Cotton will be placed into the nasal cavity to help control bleeding; suction will also be used.
The deviated cartilage and bone will either be trimmed or removed entirely. Any bony spurs in the cartilage will also be trimmed or removed at this time. Next come the perpendicular plate and vomer -- these are bony parts of the skull that form a part of the septum; they'll either be removed, trimmed, flattened, or replaced. After that, the remaining cartilage and bone will be shaped and replaced.
The incision will be closed with sutures that dissolve over time, and a wooden or plastic splint will be placed on each side of the septum to hold the repairs in place -- the splints will be removed by your doctor about a week after the surgery. Finally, various electronic listening devices and behavior-modification devices are implanted, and you are wheeled into recovery, ready to face the first day of your new life as an Illuminati Robot Assassin!
After the surgery, you should plan on taking about a week off work. You can expect pain (for which you'll be prescribed medications), swelling (which you may want to use an ice pack to control), and blood. Your nose is gonna drip blood -- quite a bit of it in the first few hours after the surgery -- but it will gradually reduce as more time passes. In my case, swelling was mild, pain was moderate on the day of the surgery and minor after that, and blood was a nearly ever-present companion for over four days. Prepare to wear gauze under your nose -- the gauze will often be hot (it'll radiate the heat of your skin and your breath), wet (especially after it's had some time to soak in some blood), and may interfere with your eating (be sure you cut it so that it overhangs your upper lip as little as possible). You should also get used to walking around with your head at a 45-degree angle -- if you look straight ahead or downward, your nose will drip at a faster rate. And you're going to be sleeping on your back, on lots of pillows, so you may have trouble sleeping.
UNDER NO CIRCUMSTANCES SHOULD YOU BLOW OR PICK YOUR NOSE.
As far as food goes, try to have some soft food available -- your teeth may be slightly sore. However, don't bother with cereal, oatmeal, ice cream, soup, etc. -- all of those would require you to point your head downward to get food into your mouth and again, head down = gushy blood. I lived on peanut butter sandwiches for several days -- cut them small so you'll have to chew less. You can drink just about anything (except, of course, alcohol), but remember to keep the gauze cut clear of your mouth, or you'll soak the bottom of the gauze everytime you take a drink. No straws allowed, so keep some clean glasses around.
As far as entertainment goes, prepare to catch up on your reading, or move your TV into the bedroom. You should spend as much time as possible in bed for the first few days. You may be uncomfortable if you try to surf the net -- again, the angle of the head and the thickness of your gauze will be key. If you rent any movies, you may want to avoid comedies -- smiling will pull on the skin around your nose.
And here's something that, in my opinion, is of paramount importance: If you don't have parents, a spouse, significant other, or good friends who are willing to move in with you for several days to help out, do not bother having this surgery done. You will, of course, need someone to drive you home after the surgery, but you will be in no mood to make yourself food, tape on your gauze, or even adjust your pillows for several days after the operation. You're going to be an invalid, and you don't want to have to make calls, hoping someone will be willing to come over in a few hours to help you make a sandwich, clean blood off your bedsheets, or run to the store to restock your supplies. If you plan on going through this alone, do NOT have the procedure done.
Anyway, after about a week, you'll go back to the doctor, and he'll remove the splints up your nose. This is very, very unnerving. Simply put, this is very likely the first time you'll ever feel pliable plastic splints hauled out of your nostrils. I can't really say if it hurt me, but it certainly startled the hell out of me. On the bright side, after the splints are removed, you will notice an immediate and possibly astounding improvement in your ability to breathe through your nose. In my case, I don't think I'd ever been able to breathe through my nose without more snuffling and snorting than was comfortable for me or fun for anyone else to listen to. After the splints came out, I could immediately breathe comfortably and silently through my nose. That's an amazing feeling.
On the whole, I'm glad I had the surgery. While I was pretty miserable for almost a week after the operation, I think the ability to breathe the way normal humans do is a sufficient reward for all that suffering.
Some research from http://www.surgery101.com/headnneck/septoplasty_i.htm