There are three major credit bureaus: Experian, Equifax and TransUnion. Each collects information on your credit history which is culled into a credit report. From that report, a credit score is derived. That score is a quick way for lenders to assess how risky you are as a potential borrower. The higher your score, the less risk you pose to lenders and the more likely it is that you'll get their best available rates.
The score most commonly used by lenders is the FICO score, developed by Fair Isaac.
When you get your reports, check for inaccuracies; the bureaus are required to investigate and correct them once you report them.
The bureaus may have different information about your credit history, which means your credit score can vary somewhat from bureau to bureau. So it's important to view reports from all three.