There are three things that you should look out for when checking the oil level quality and they are the oil smell, color, and consistency. The motor oil is mostly light-colored and transparent but with time, it becomes dark, thick and gritty and there is a change in the consistency, when this happens, it calls for an immediate change. Usually the oil filter keeps the dirt and combustion by-products at bay but this is just for a short period of time. However if the color is light brown and milky color, this indicates that radiator is leaking and the car should be towed. Also, if the oil smells like gasoline, there is a 100% probability that the entire engine needs servicing. 

Checking the oil level capacity requires that the car is turned off with the keys off the ignition point and parked on a leveled ground so that the oil is evenly distributed, hence an accurate reading. It is preferable to allow the engine to cool off and settle for few minutes to prevent you from sustaining a burn. Afterwards, pop the hood and locate the oil dipstick which is usually a long metallic rod located on the side of the engine depending on the vehicle and if it is not easy to locate, you can always refer to the manual. Pull out the dipstick and wipe with a towel, insert back into the dipstick lube and wait for few seconds before pulling out again and read the level. At the end of the dipstick has an operating range indicated by low and high, or max and min, if the oil does not reach the operating range, it calls for a change.