To squander means to spend extravagantly, thoughtlessly, or wastefully. If you need to save for college, don't squander your income on nightly sushi dinners.
Squander used to mean scatter, and the way we use it now implies throwing something (like money) all over the place. You can squander time as well as money. If you have a big deadline but you are chatting away or looking at social networking sites, you are squandering your time. If you have a big chance to play for a major league baseball team, but show up to the tryouts hung over, you have squandered your chance.