What does 0% apr for a year on a credit card mean?

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I recently got a new credit card through my grocery store since I moved out and need to save money on stuff like that now (hehe) and it says I have 0% apr until July 2014. I have always paid off my balance at the end of the month for my one other credit card, so I'm not sure quite what that means, but I do want to buy a desktop computer since my boyfriend is always on his and I waited and found one that is on a HUGE sale for $600!!! (It's a gaming computer, and the sale is only for two weeks) I am plum out of money from moving except for my emergency funds which I don't want to dig into, but I really don't want to pass this offer up.


I figured already that it means no interest, but if I decide to buy it now and don't pay it completely off until 3 months later, will I get charged interest suddenly for it next july? And will this affect my credit score?

What does 0% apr for a year on a credit card mean?