There are two major differences between cash games and tournament. The first is, that in a cash game the "chips" on the table maintain the same value always. If you win all the "chips", you win all the money, very simple. In the vast majority of tournaments there is a payout structure, so even if you win all the chips, you dont win all the money.
This mean, that the value of the chips go down, as you accumulate them, so winning chips is not as good, as losing chips is bad. This is often referred to as ICM (Independent Chip Model) and generally reward a more conservative playing style especially when it come to not calling all in against another player.
The other main difference is, that the size of the blinds change in tournaments, and after the first few blind levels stacks tend to get short. Just how short depend on the structure and starting stacks, but typically most tournament hands are played with less than 100BB stacks. This make the game simpler, and the shorter stacks get, the more difficult it become to make huge mistakes. Typically this lack of experience with deeper stacks is why, tournament players often do poorly in cash games.
Finally there are usually antes in tournaments but not in cash games, and when there are antes, you need to play more hands to not get blinded away. So its a way to force players to not play so overly tight, as would otherwise be the winning strategy in tournaments.[/QUOTE
That was very helpful. Thank you!