What information do I tell a personal trainer about myself?

As much as you want. They will ask you some questions - and you may choose to not answer them if it makes you uncomfortable in any way. Tell your trainer your goals, your past success' and failures, your prior injuries (if any), and your "barriers" which are the things that seem to get between you and great fitness. That will help the trainer help you. The rest you can 'play be ear'!