We use imperatives for different reasons, such as telling people what to do, giving instructions and advice, making recommendations and suggestions, and for making offers.

For example:

			Come in and sit down, please.
			Don't open the window - it's cold.
			Put the coin in the slot and press the red button.
			Don't ask her - she doesn't know.
			See the doctor - it's the best thing.
			Have a bit more wine.

taken from here