Your credit report shows what information is currently held about you and your finances. Your credit file is accessed by banks, credit card companies and other money lending firms to decide wether or not to lend you money and if you are approved for a loan, how much interest to charge you. To access your own credit file, you need to send a request to a credit reference agency.
Based on your account management (paying bills on time, not exceeding your spending limits on your credit cards) credit agencies will also give you a credit score. When looking to apply for a loan with a high or good credit score, you should expect to get charged a lower interest rate compared to having a poor or low credit score. For UK residents, there are four credit agencies which update your credit report:
Some sites and credit agencies will charge you to provide your credit report and credit score information. I've gone ahead and included a couple of sites which provide your credit score and report for free!