Annual Credit Report is a website that allows you to pull your credit for free once a year. You won't be able to get your credit score for free, that you'll have to pay for; however you can run a full report from each of the credit reporting agencies free of charge.
So why is this important? Well, your credit is what determines your interest rates on loans, whether or not a financial institution will lend you money or how much they'll lend you, whether you can get a car or a house and whether or not you can get those things at decent interest rates. Plus, some jobs require good credit in order for you to be considered for a position. Your credit is so important for your day to day life, it's important to make sure that it is accurate.
The nice thing is the website is fairly easy to use and if you do find some discrepancies on your reports, they (the three credit reporting agencies--Transunion, Experian, and Equifax) all have instructions on what you can do to fix it. There is no reason why you shouldn't take a few minutes out of your day to make sure your report is accurate, it's too important not to. Plus, like I said, it's free with no gimmicks (unlike those ones who claim to be free but make you sign up for 30 days with a credit card) or hidden agendas.
Hopefully this was informative, make sure you pass this link along to family and friends so they can check out their own credit reports!