This is the most basic maintenance task, but many people do it wrong. Here is the correct procedure.
1. Park on Level Ground
If the car is on a slope, the oil will pool to one side of the pan, giving you a false reading.
2. Ensure the Engine is Cold
Wait at least 10-15 minutes after turning off the engine. This allows all the oil to drain back into the pan.
3. Pull and Wipe the Dipstick
Pull the dipstick out, wipe it clean with a lint-free cloth, and re-insert it fully.
4. Read the Level
Pull it out again and look at the end. The oil level should be between the MIN and MAX marks. If it's below MIN, add oil immediately.