Here are links to two Youtube videos that you might want to view. Offered by IntownBicycles, they show how to repair a flat tire and how to remove and replace your rear wheel:

http://www.youtube.com/watch?v=FzqjoFAXA5I

http://www.youtube.com/watch?v=Mfu96dIcPdA&feature=channel

Steps to Repairing a Flat Tire

1. 1. Alert people you are riding with that you have a flat before stopping. even if you are not sure. Don't stop without telling your partners. Then find a safe place to perform your repair. Remove your spare tube, pump and tire levers from the bike.
2. Release or open the brakes. Even if the tire fits through the brake shoes, open them because once the tire is fully inflated it may not fit and will interfere with your efforts to reinstall the wheel to the bike.
3. For the rear wheel, first shift to the smallest cogs on both the front and rear of the drive chain, giving the chain maximum slack. Remove the wheel by releasing the quick-release lever. For the front wheel, unscrew the quick release a few turns to allow it to pass the retention tabs on the fork. For the rear wheel do not unscrew the quick release, just release. The rear wheel should drop out of the frame with the quick release and the brakes open. Putting rearward tension on the rear derailleur moves the derailleur out of the way and it should drop out.  If it does not drop out on its own, it should drop out by just tapping the top of the tire. When the wheel is removed, lay bike on its left (non-drive-side) side so to protect the drive chain from damage.
4. Pry one bead of the tire from the rim. Here are some tips to make this easier. First try to release as much of the remaining air from the tube. Second try to walk as much of tire toward the area you are working. Do this by working from the opposite side; pinch the tire to make it sit close to the bottom of the rim all the way from the opposite side toward where you are working. Doing this allows you to pull the bead away from the bottom of the rim, giving you more space to get the bead over the edge of the rim. Then move around the edge of rim, prying the tire over the top using your tire levers. In order to keep the bead from slipping back over the rim, attach the tire lever to a spoke to free one hand. When the bead is off all the way around, we are ready to remove the tube.
5. Before removing the tube consider taking this opportunity to locate the puncture site. You may already have found a thorn or piece of glass. If so, when you remove the tube, mark the tube in some way to make it easier to locate it when patching it. If you are not going to patch it you still want to determine the cause of the flat. If it is not obvious, there are two options. You can pump some air into the tube and try to see or hear where it is leaking. If you find it, look for a problem with the tire or rim at the location of the leak. You can rub the inside of the tire, feeling for sharps. Or inspect the rim strip under the location of the flat for a problem. If you fail to find the cause of the flat, you can only cross your fingers that you did not miss something.
6. The tire and tube will come off as one unit if you remove the tire from the opposite side from the stem.
7. If the tire has damage that would allow a tube to push through (aneurysm) you can temporally strengthen the tire with a tire boot. A  tire boot can be made by cutting up an old tire. You can also purchase boots to carry in your tool kit. If you need a boot but do not have one you may be able to get away with using a dollar bill or a wrapper from an energy bar. A booted tire is only to get you home and then replace the tire.
8. Insert the new tube. Put a small amount of air into the tube first, just enough to give so it is not a noodle. Time to insert the tube into the tire. Two ways to proceed. The first way is by first mounting one bead of the tire onto the wheel first, then inserting the tube. Pinch the tire where the stem goes and place the stem into the hole. Install the washer to the stem (Presta only.) Begin placing the tube at 180 degrees away from the stem, then work back toward the stem along both sides of the rim. The alternate method is to place the tube into the tire first and then mount tire and tube together onto the rim. After the tube is in place, begin prying the bead over the edge of the rim, beginning 90 degrees from the stem working in either direction. As you get close to seating the last of the bead it gets more difficult. At this point it might help to release some of the air from the tube. Also use the same technique as when you removed the tire by pinching the tire together at the opposite side of where you are working and walking the tire along the rim towards where you are working. This will only work if you release all of the air from the tube. It is generally considered best to avoid using your levers to pry the tire onto the rim because this often causes the tube to be pinched, resulting in a puncture. You should use your hands to force the bead over the top of the rim. Some of these techniques may be unnecessary if your tire mounts easily.
9. Once the entire bead is on the inside of the rim you need to make sure it properly seats. You can help this process by pinching the tire together and running the length of the tire. Then inspect the bead for bulges caused by the tube lying between the rim and the bead (a bad sign). You can now do a pressure trial of 20 to 40 pounds, depending on type of tire. Pump up the tire about one quarter recommended pressure. If using a Shrader valve, push against the bottom of tire toward the pump until there is enough pressure to keep the tire pushing against the pump. Remove the pump by popping it off -- smack it downward smartly, don't pry the pump off. Inspect the bead for presences of bulges. If it is very close to being even all the way around without any bulges you can continue to inflate to recommended pressure. When finished, inspect the bead one more time.
10. The washer for the stem will need to either be tightened down finger tight to the rim or removed completely. It is there to make initial inflation easier. You can replace the wheel onto the bike now. For rear wheel, move the derailleur out of the way and lay the top of the chain onto the top of one of the smallest cogs. Make sure the tire clears the brake pads and guide the quick release edges into the frame. When closing the quick release, have the bike standing up square, which will help ensure the wheel sits square in the frame. For the front wheel, you will have to tighten down the quick release prior to closing. Have someone show you the proper position before trying this by yourself to avoid front wheel falling off while riding. (Yes, it happened to me once.)
11. Close the brakes shoes back to operating position.

The first time you have to do this by yourself on the road it might take you 30 minutes or more. With practice it can be accomplished in as little as five minutes. Practice at home before going out to ride solo with no road service available. (One additional tip for practice only, when deflating a Presta tube, make sure the valve washer is loosened or removed prior to deflation to prevent damaging the tube.)