APR is an abbreviation for Annual Percentage Rate; therefore APR is simply a description of the interest rate for the whole year, so it gives you a clear idea of the interest rate on a long term basis rather than just a monthly basis. However it should be noted that APR considers not only the interest provided on the loan, but also it included other additional charges that must be paid, for example arrangement fees, it is best to check with the provider what other things are included under the additional charges that will be included under the APR %. So for example an interest rate could be 11% per year (annum) but then the APR could be 19%, therefore the extra 8% would include the additional charges. So it is the APR that is important to be aware of, but all loan providers are under an obligation to inform you of the APR %.
But when comparing providers, it is easier and more common to consider the APR; because at the end of the day, this is the % that you will be paying. Additionally, companies are unable to hide additional charges, as any additional charge will be included in the APR; furthermore it is easier for you to compare various loan providers to get the best deal for you!