When checkin the oil level, always let your car sit for a couple of minutes for the oil to drain back down to its resting level.
You can check your level warm, cold, whatever....just know where to look on the dip stick.
When cold, you want the level to be as close to F as possible (between L and F you're pretty much good)
When hot (like if I've been driving for an hour and stop at a gas station) the level usually is close to or at the full when hot marker (a small concave indentation)
When filling your engine, I run my engine till it warm so as much old oil will drain out as possible (don't burn your fingers removing the nut). After filling, which I don't usually pit in the full amount right away, I run the engine (not drive it) for about 5 minutes, and let it sit for about as many. Then I fill to the F mark.