There are two simple ways to calculate your hand odds. Harrington mentions one, figuring out the number combinations of possible hands based on the # of cards in the deck of that type/combination and then calculating your hand against that range.
The other way is
this where you can play around with various scenarios putting your hand against a range of hands or a specific hand if you narrow down the range that far. After a while, you will begin to remember odds for hands like AK v 55 or whatever while you are playing.