Insurance is just an option. You can play without using it, it just affects the risk. If you're having trouble there's a simple explanation on
BlackjackInfo which goes into how it works.
The idea is that if the dealer shows an Ace they will offer insurance as an option. Players can make a second insurance bet of half their original, which pays out if the dealer has a blackjack. Unless you are counting cards, most places say it's only really worth taking it if you already have a blackjack, since it is pretty much just a bet on whether the dealer has blackjack. It's not something I take that often.