And if you are comfortable with a little algebra, here's the formulae that tie things together:

The probability of an event happening = p (fractional)
The odds (against) = w as in w:1 "doubleyou to one"

w = (1-p)/p

p = 1/(1+w)

If you throw in the number of ways you can lose (not draw the card you want) and the number of ways you can win (draw that nut flush!) then

p = (#of wins)/(#of wins + #of losers)

w = (#of losers)/(#of wins)

Play with the numbers and you'll see, for example, that if p is greater than 1/2, w will be less than 1; this is a positive liklyhood of winning so less than even money (1:1) is good pot odds. (Doesn't happen very often!)