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.