Changing the oil in your own vehicle is a relatively simple task that can save you money, provided you don't mind getting a little dirty. Before you get started, however, you need to do a little homework and possibly purchase a few tools.
First off, consult your vehicle owner's manual and see what kind of oil your vehicle requires. This is often listed on the oil cap under the hood as well. Next, visit your local auto parts supplier and make sure they have the proper oil filter for your vehicle. The vast majority of modern vehicles use a standard screw-on type of oil filter. If you're vehicle uses a different type, I'd highly recommend letting a repair shop do the oil change, since these oil changes can be far more complicated. Purchase an oil filter wrench that will allow you to remove the oil filter from your engine. Make sure you get one that will fit your particular filter, since they vary in size.
Strangely, owner's manuals do not list the amount of oil you need for your vehicle, so you'll have to estimate. Six quarts is usually more than enough, and you can save any unused oil for the next oil change. Additionally, you'll need some ramps to pull your car up on so you can get underneath it, a drain pan, a set of metric or standard wrenches, depending on your vehicle, a funnel, and a few rags. You'll also want to make sure you have a level concrete surface to work on.
Start by pulling your vehicle up on to the ramps. Never use a jack to change your oil. It could collapse and injure you severely. Apply the parking brake and place a chock behind the rear wheel to keep the car from rolling backwards. Next, get your drain pan and wrenches and slide underneath the front of the vehicle. Loosen the drain plug for the oil pan and allow the oil to drain into the drain pan. The oil pan is located directly under the engine. Take care not to confuse it with the transmission fluid pan. On a rear wheel drive car, the oil pan is in front of the transmission pan. On front wheel drive vehicles, the oil pan is typically centered and the transmission pan is off to one side.
A quick note about drain plugs: Never use a socket or a pair of pliers to remove the drain plug. These can slip and round off the corners of the plug head. Only use a properly fitting wrench.
Once the oil is drained from the pan, screw the drain plug back in taking care not to cross-thread or overtighten the drain plug. Next use your oil filter wrench to loosen the oil filter. You may have to look around a bit to find the oil filter, but on most vehicles, it's located next to the oil pan. Loosen the oil filter and let the excess oil drip into the drain pan. When most of it has drained out, remove the oil filter carefully, because it may still have hot oil in it.
Before installing the new oil filter, apply a small amount of oil to the rubber gasket on the top of the new filter and make sure that the old gasket came off the engine with the old filter. Tighten the oil filter hand tight. Do not use a filter wrench, because it can damage the filter. Use the rags to wipe off any excess oil that may have spilled.
You're now almost ready to add the oil. Get in your car and without starting it, place it in neutral and allow it to slowly roll back off the ramps so it's sitting level. Keep your foot firmly pressed on the brake pedal since it requires more pressure to the brake pedal to slow a vehicle that isn't running. Never start your car without oil in it! This can severely damage your engine.
Once the vehicle is on level ground, open the hood and place the funnel into the oil filler neck. If you have a four or six cylinder vehicle, pour four quarts of oil in. If your vehicle has eight cylinders, five quarts is a good starting point. Screw the oil cap back on and go start the car.
While the car is running, quickly look underneath to make sure no oil is spewing out where the oil filter was installed and then shut off the car. If everything looks good, go back around front and remove the oil dipstick. Wipe the oil off the end of the dipstick and reinsert. When you remove the dipstick this time, look and see where the oil level is. There should be an area at the bottom of the dipstick that says "Oil Fill Level" or something similar. It should be about an inch wide. When the oil is at the top of this area, the oil pan is sufficiently full. When it's at the bottom of this area, the oil level is too low and more should be added. Typically, a quart of oil is all that's needed to go from the bottom of this range to the top, where the oil level is perfect. Take care not to pour too much in, as this can also damage the engine.
When you think you have it right, restart the engine briefly, then shut it off and recheck the oil level. If everything is okay, pour your waste oil into the empty oil containers and dispose of it properly, at a recycling center or auto repair shop. Clean up any mess you may have made and record your vehicle mileage. You're all set for another 3000-5000 miles and you've probably done all this for about $15. A lot better than $50 a dealership might charge.