IMPORTANT: never attempt to drive on a flat tire. You will throw your vehicle's wheels out of alignment, ruin the expensive tire, and bend the expensive rim.
ALSO: use sealing gunk containers only when you are absolutely stranded and don't mind spending $100 on a new tire. They ruin the tire.
1. Assess damage of the tire and make a note of where it happened. Do not drive over that spot again.
2. Locate the jack and jack equipment in your vehicle (usually hidden under seats or under a false bottom or false wall of a car trunk.
3. Using the tire iron or wrench, loosen all lug nuts on the flat tires wheel (righty tighty, lefty loosy--turn counter-clockwise). If you try to loosen the nuts after lifting the vehicle, the wheel will rotate, making them very difficult to remove.
4. Follow instructions on the side of the jack. Usually there is a picture showing where on the vehicle's underbody to place the jack. If there is none, the frame of a small car or the axle of a Sport Utility Vehicle will do.
5. Connect the crank assembly to the jack and rotate clockwise until the flat tire is a few inches off of the ground.
6. Now remove all lug nuts from the wheel and remove the flat tire.
7. If not already known, locate the spare tire. In a small car it will be a "donut" or miniture tire in the same trunk compartment as the jack or in the false floor compartment. In a Sport Utility Vehicle it will either be on the inside of the vehicle (jeep) or on the back hatch (Jeep, Nissan, Mitsubishi, etc). Remove it.
8. Slide the spare tire carefully onto the lug nuts making sure not to damage the threads. Hand tighten the lug nuts and finish off with the tire iron or wrench. Tighten each a little first working in a circle before tightening all of them completely. Do at least two rounds.
9. You are finished. Put away the tools, and drive to a garage or gasoline station to have the flat tire plugged. This is usually fairly cheap ($10-20) and quick (maybe 1/2 hour). The mechanic will then put the new tire onto your car.