Grand Prix Performance - Costa Mesa, CA

Place your car at the level spot. Stop the engine. Wait for a while to let the engine oil to pour down to the oil pan. Pull the engine oil dipstick. If you don't know where is the engine oil dipstick, check your owner's manual, usually it has a bright handle saying "engine oil".

Wipe it off with a clean rag or tissue. Then insert it back all the way down into its place.

Now, pull the dipstick again and check the oil level. Normally it should be at "FULL" mark. For example, here you can see that it's a bit lower. It's not a big problem yet, but it's better to top it up. Check the oil condition: If it's way too black, it's definitely time to change it. If it's slightly-brown, it's O.K. If it's dark-brown, but still transparent, it's admissible but it's better to change it soon. 
If it's white (coffee with milk color) it means the engine coolant mixes with the engine oil because of some internal engine problem, for example, blown head gasket - have your car inspected.

How to top up the engine oil: 
It would be better to add the same type and brand of the engine oil as you already have in the engine. Add a little amount of the oil as it's shown in the image. Wait for a minute to let the oil to pour down. Check the oil level again with the dipstick. If it's still low, add some more. But don't overfill it. Don't forget to install the dipstick back and close the oil filler cap when you finished.