A new card with a 0% introductory APR lets you make purchases without incurring any finance charges during the promotional period. However, these cards do still require a monthly minimum payment. Failure to make a monthly payment will cause you to default on your cardholder agreement, and your introductory APR may turn into a penalty APR and you can be charged a late payment fee - so never miss a due date!
The best thing about a 0% intro APR credit card is, obviously, the interest-free introductory period! You'll pay no interest for several months after your account is opened, depending on your offer. But be careful to pay off your card balance in full by the end if the introductory period because once it ends, an ongoing interest rate will apply to your unpaid balance and future purchases. Some issuers even charge interest back to the first day of promo period.
Another good feature of the zero interest credit cards is a rewards program. Many issuers allow to earn cash back, points or miles on purchases. Also, Visa, Mastercard and American Express cards all have purchase protection plans on items bought with their cards - so, if your fancy new computer goes on the fritz, your credit card company may refund you even if the store won't.