Implied odds are the ratio of the total amount of $ you expect to win if you make your hand to the bet you must now call to continue in the hand.
So lets say you have 89 and the board is:
You are pretty sure your opponet has an Ace or even two pair.
Lets say you both have $100 in front of you and there is a $50 pot. He bets $30 to you...
If you make your hand, you figure he will most likely push all of his chips in. So your implied odds are 150:30 or (you will win $150 ($50 in the pot+ $100 he has) if you call his $30 bet).
So you have 5:1 implied odds.
To caluculate the pot odds
in this situation you take the # of outs you have (8) and divide by the # of cards unseen (45).
You are getting 5.625:1 pot odds on hitting your straight draw.
It is a close call, but in this situation I would not make it.