Apple hardware comes with a one-year warranty. You also receive free phone technical support for up to 90 days after buying a product. At any time before the one-year warranty expires, you can buy an AppleCare Protection Plan - with one exception. But I'll get back to that.
What exactly do you get with AppleCare? An extra two years of hardware service and phone support for Macs and computer displays. The gadget plans provide an extra year of coverage for your iPod or Apple TV.
But do note that you don't buy an AppleCare "plan" to cover all your "iTems." It will include the computer display and router if they're bought at the same time as a computer. Otherwise, you purchase AppleCare separately for each product you buy. Prices vary based on the product. As an example, AppleCare for an iMac is $169.