This page contains actual surgery photos and describes the surgical procedure:
http://www.thepetcenter.com/sur/sp.html
Some vets recommend six months so that sex hormones from the ovaries (or testicles, for males) can influence the puppy's growth. It also is easier for vets to operate on a six-month-old than a tiny little eight-week-old, though many vets are comfortable doing pediatric spays and neuters.
At my vet (and clinics and doctors differ, so this may not necessarily apply for you), they have me drop off my pet before 9:30 AM the day of the surgery. For cats and dogs, they usually have been denied food and water since midnight, so they don't vomit after the surgery. The surgery is usually done and my pet awake around noon, and the vet calls to let me know how things went. Depending on the pet's condition, reaction to anesthesia, etc, they may keep her overnight or let me pick her up that same day. Shelby the kitten stayed overnight, Holly the rat came home with me just a few hours after she woke up. When I go to pick up my pet, the vet speaks with me about home care--if yours doesn't, just ask! I'm sure they'll be happy to do so. Usually I am told to try and keep my pet from jumping, which can irritate or open the incision, and to watch for excessive redness, oozing, or pain indicators. I haven't ever had to do anything specific for aftercare.
Hope this helps--I have never had a dog in my care spayed (they're rescues and came to me already altered), but I have had two of my cats and one of my rats spayed while in my care. Best of luck.