Starting with Engine Oil
Chances are, the first thing you ever learned about on your first car was how to check your oil. You have to do this in every car and pretty much every car has the same basic process to check it. Every car though has it in a different place, so double check your manual if you can’t find it.
In most cars, you just need to pop up your hood, find the oil dipstick, pull it out, and wipe it down. Repeat that again and you'll have your oil level. If it's in the safe level, continue on your merry way. If it's not, you need to add more(make sure you know what type of oil you should be adding). Depending on the age of the car, you may or may not need to add oil pretty often. If your car burns through a lot of oil, it's worth going to a mechanic.
How often to check it: It was once recommended that you check your oil every time you fill up with gas, but with most modern cars you're safe checking it once a month.
How often to replace it: This depends on the car, manufacturer, year and how you drive your car. The "3,000 miles or every six months" saying doesn't really apply any more. Instead, check your owner's manual for the manufacturer's recommendations for changing your engine oil.