Experian are a credit reference agency. They give you a little score that lets other creditors know whether you’re a good risk for lending money too, getting a credit card, mortgage, etc.
You can get a paper report for close to free still I believe. Equifax and Experian charge a monthly fee. I just use ClearScore which is free and shows all your credit outgoings, debts, account, defaults, county court judgments, and a score.
I imagine companies that use them to check potential customers pay a fee.