There should usually be two marks on the dipstick, the one near the bottom is the low level and means never go below this level, the one further from the bottom is the high level and should not be overfilled past this mark, please note that more oil is not better and overfilling can cause problems for your engine. Anywhere between the marks is OK, check it with the engine cold.
While you are at it you might also want to check the gearbox oil level which is also a dipstick in the engine compartment, but this is usually checked with the engine hot.