You did not mention the make and model in your question. Therefore a difinitive answer is not possible.
It varies but usually:
Button in = High Heat
Button out = Low heat
If the button is marked 'cool' then 'in' will activate that option but it may be to activate a final cool tumble for easier ironing.
If the button has a couple of strange pictures, one for in and one for out, then the one looking closer to a T-shirt is the hot position.
You will need to check the operation guide for the purpose of a button marked 'cool' and whether this means that the temperature changes or whether it substitutes a final cool tumble for easier ironing.
Neil S, November 2013
