Even though cars are complex machines, maintaining a car isn't as difficult as many think. Working on a car yourself can help you save money, especially if you know you don't need what your mechanic would be trying to sell you. Remember, if anything on this page doesn't go into enough detail or if something appears to be missing, you can check the full maintenance and repair section for more detailed information. Always work on the vehicle with the engine off and cooled down! If you don't know what you're doing, ask a professional.
Engine Access
You will need to access your engine for many maintenance procedures. Lifting the hood/bonnet (or trunk/boot in vehicles with the engine behind the driver) will first require you to pull the release lever, which is usually located under the dashboard, on the driver's side, near the pedals. After you unlock the latch that holds that cover down, and there will usually be a second latch (that varies from model to model) you will have to lift to get it completely open. Most of the time, the hood is held open by a rod found in the engine compartment, but some cars have pneumatic rods which do this job.
Checking Your Oil
After waiting for your engine to cool down, locate the dipstick. This is usually a yellow loop just big enough for one finger to fit through, but is sometimes a different color or metal. Once you pull it out, wipe it clean with a disposable cloth/rag, and put it back in all the way (all of this is necessary for accuracy). After taking it out the second time, look at the level, as well as the oil's condition. There should be a marking on the dipstick which notes what is a good level. If it's too low and the oil is in good condition, you can add oil, but make sure it's the same type as your current oil. If you are familiar with the smell of clean oil, you can smell the oil to determine its condition. If it's unusually foul or smells burnt, you will need to change your oil.
Checking Your Air Filter
In the engine compartment, the air filter can be found in a number of places, depending on the vehicle. A lot of modern vehicles have it hidden away in a moderately large black plastic box on one side of the engine, but some cars (particularly older cars) have their filters out in the open, or in a round container directly on top of the engine. If you're not sure where it is, your driver's manual should tell you where it is.
Engine Coolant
In most cars, you can check the coolant level by looking into your coolant container, looking for coolant. You can top it off with water if it appears low, and you can smell for it if you remove the cap (antifreeze has a sweet smell to it). If there is oil in your antifreeze, it is likely a broken gasket, which creates a passage between the cooling and oil paths, and this can be very bad for an engine if you continue to drive it (since coolant is also likely leaking into the oil). Antifreeze is important for both cold and hot conditions. It doesn't only lower the freezing point of the water; it also raises the boiling point, making it more effective at temperatures above 212°F (100°C). It also serves as an anti-rust chemical; without it, your radiator might rust to the point of leaking.
Tire Inflation
Tires don't have to be inflated exactly at the recommended pressure, but in most cases it's best when they are. Air pressure in the tire keeps the sidewalls stiff enough to hold up the weight of the vehicle, and the middle of the tread on the road. Overinflation can expand the tire too much, which can result in either a blowout or too much wear in the center of the tire's tread. Underinflation can weaken the sidewall and wear out the tread near the edge of the tire faster than the middle. Having your tire slightly below the recommended level can improve grip (especially when driving through dirt) but adds rotational drag, which reduces fuel economy. Setting the pressure slightly above isn't recommended, but could improve fuel economy; however, since this reduces tire life and could result in a blowout, there is no money saved when overinflating.
Spark Plugs
Spark plugs are found at the end of wires which appear to go into the engine, but get thick just before that point. Depending on your engine layout, they may be all on one side of the engine (in the case of the inline design), or along both sides. On a Wankel Engine, they are on the opposite side of the intake and exhaust manifolds, and Diesel Engines don't have spark plugs.
Brake Pads
Brake pads are quite durable, but will need replacing from time to time. Many modern brake pads come with built-in wear warning indicators which will cause your brakes to squeak before they are completely worn out (which arguably saves a great many lives). Both disk brakes and drum brakes use brake pads; drum brakes will have a rounded contact surface and disk brakes will have a flat contact surface. Replacing old brake pads with thicker, newer ones (all brake pads get thin with wear) will require some of the brake master cylinder fluid to be removed, which allows the brakes to move far enough away from the disk/drum to fit the new pads. Changing either both front, both rear, or all four brake pad sets is recommended (not just one pad, one set, or all the pads on one side) to avoid braking level imbalances.
Battery Maintenance
Not much can be done to help a dying battery if it has an actual problem, but if your alternator is going bad, you can charge the battery back up with a jump from another car or a charger (designed for 12-volt car batteries) as a temporary fix. Cleaning off the surface between the connections can prevent some charge loss. Make sure you don't touch both connections at the same time! Try to avoid touching them altogether. If one of them has a crusty teal/white material on it, it could be a sign of a problem with the battery.
Windsheild Wipers
You can usually tell when it's time to replace these, because they won't do a good job wiping water off your front window. However, you can check them for smoothness by (gently) pulling them away from the window (on most, but not all cars) and feeling the contact area, which should be completely smooth. A worn wiper blade will have small chunks missing or cracks. Most wiper blades have two options for replacement: pulling out and replacing the rubber component, or replacing the entire assembly. Some special wiper blades, however, require replacement of the entire assembly. Getting the standard kind and only replacing the rubber section is the most financially-optimal way to go.