IRS sent me a letter asking for a copy of page 1 and 2 of my return and supporting documents verifying income and withholding. Why do they need those documents?

Every now and then IRS asks for this type of thing, whether its a random spot check for accuracy or something in your records doesn't add up, nobody could tell you for sure....just send them what they are asking for.

How do I know what supporting documents I need to send? Is that just my W-2?

Sounds like they are requesting copies of your income documents, so any W2 or 1099 forms that you included on the tax return....if all you had was a W2, that's all you would send.

Since you are asking from TT Self-Employed, they may want to verify your cash income as well.