If you've never requested a credit report, then you'll need to go to annualcreditreport.com and request a copy of your report from the big three. You get a free copy once a year. Any other time, it costs about $7 to $10 dollars, depending on the site you use.
If you aren't on file, however, you'll have to print out the form and send it to them with proof of address/and picture I.D. I sent in a photo-copy of my license, SSI card, and phone nill to do this. Have it notorized to show it's a direct copy of the original.
As far as fighting what's on your report, I'd need more information. The do tell you/give you a form to protest it, but as to how to "win" the protest, that's another story. How old is this debt? There are statute of limitations on credit debts that vary state by state, usually from 6 to 12 years. Anything past that date can't be collected on, IF you don't respond/acknowledge the debt.