How do I get IRS to explain why they have audited me?

Are you in fact being audited?  For what tax year?

Or are you under review or are they requesting that you verify identity?   

I RECEIVED A LETTER FROM THE IRS/STATE

TurboTax does not receive any information from the IRS or your state after your return was filed, so no one at TurboTax knows about a letter you received from the IRS or the state.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-audit/turbotax-audit-support/L6AcMoNFD_US_en_US?uid=m5z7by9u

https://ttlc.intuit.com/turbotax-support/en-us/help-article/internal-revenue-service/got-cp2000-notice-irs/L7Da6em2t_US_en_US?uid=m4of6ngd

I RECEIVED A LETTER FROM THE IRS/STATE

TurboTax does not receive any information from the IRS or your state after your return was filed, so no one at TurboTax knows about a letter you received from the IRS or the state.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-audit/turbotax-audit-support/L6AcMoNFD_US_en_US?uid=m5z7by9u

https://ttlc.intuit.com/turbotax-support/en-us/help-article/internal-revenue-service/got-cp2000-notice-irs/L7Da6em2t_US_en_US?uid=m4of6ngd

They should send you a letter that tells you what they need or are changing. The type of letter also gives you information. To see the IRS website for types of notices and what they mean, click here.

The letter you receive should have a contact method.

Please see I received a letter from the IRS for full TurboTax instructions.

If this audit creates a financial hardship for you, contact the Taxpayer Advocate Service or call 877-777-4778.

If it is actually an audit, the IRS will tell you what items on your tax return they are auditing, but they will not tell you why. They do not discuss what criteria they use to select tax returns for audit.