My bank statement reflects a completed withdrawal of $25 "uncollected funds charge IRS USATAXPYMT" how can they take unauthorized $ from my bank? And what is that for?

Yes, the IRS can draw from your account without your prior authorization.

If your haven't already received a Letter 608C from the IRS, then you will be receiving one explaining the $25.  If your payment to the IRS was to be for less than $1,250, then $25 is the penalty imposed by the IRS if your payment to the IRS was dishonored/rejected by your financial institution.  If your payment was to be for more than $1,250, then the penalty is 2% of the amount of your payment.

See Tax Topic 206 - Dishonored Payments  on the IRS website at:
   https://www.irs.gov/taxtopics/tc206.html