play in freerolls for a few years until you learn the basics
The difference between tournaments and cash games, is in cash games you mainly only care about winning chips, so any bet with a positive EV is generally OK.
In tournaments, you not only care about winning chips, but in surviving as long as possible in the tournament. That makes some strange things happen, sometimes a plus EV in winning chips is not enough to compensate for increasing the risk of busting out of the tournament.
Even stranger, if one is a very bad player, sometimes a negative EV as far as winning chips goes, actually gives a better chance of winning the tournament