Thanks!! yes, notaprof, please let me know if the process is still the same.
I was there this summer. Just walk up to the kiosk (it's before you get into line to go through passport control [I guess that's obvious]) right by the start of the line.
Walk up, hand them a $20, they'll look at you through the glass and stick the sticker in your passport and stamp it. It's totally easy.
There was a brief time when it was around $100, when the USA raised our visa price on Turkey. They're symmetrical.