This is one car maintenance practice that hasn't changed much over the years. Just about anyone can do it, and it has the added benefit of getting you to lift your hood and actually see what your engine looks like.
Most of the engine will be encased in some kind of cover with a lot of wires and hoses coiled around it. But somewhere in there, usually toward the front, you'll find the dipstick. It likely has a loop or hook on the end for pulling it out.
When the engine is cool, pull out the dipstick and wipe off whatever you find on the end with a towel. Notice the markings at the end of the stick -- the minimum and maximum levels are marked, sometimes with crosshatching between them or even holes in the metal. Put the dipstick back into the engine and pull it out again. Now check to see where the oil level is. It should be closer to the maximum than the minimum, but not over full.
It's okay if the oil is brown or black; that just means it's doing its job. Replace the dipstick, wash your hands, and feel good that there's still something in the engine compartment that you can take care of.
Wait -- was the level low? Well there's more you can do, then. Keep reading to find out how to safely add oil to your engine.