Sometime odds are expressed bit differently, but it's a simple concept.
Imagine Zim and Aus are going to play 100 ODIs. I can say that odds of Zim winning is 5% or 1 game out of 20 games. It can be also expressed as Zim - Aus odds are 1 - 20 . It doesn't matter how we express it, it's a simple probability of one team winning. Now you can come up with very off target odds , but bookies are generally right on target to come up with correct odds due to money involved. Since Zim's chance is only 5% against Aus, you can bet money on Zim and if Zim wins then you make lots of money. Placing bets on Aus will not make you much money because Aus is anyway expected to win. Bookies don't lose much money and main reason is that they are pretty good with calculating odds.
Hope it helped a bit.