The border
Also be prepared have your photograph taken and to be ‘ten printed’. Which means fingerprints for all 10 digits will be taken. Usually right 4 fingers in one time then the thumb then repeated for the other hand.
You must have documentation showing your onward travel from the USA. Strongly recommend printing this out rather than relying on your phone. Wifi is usually crap at customs if it’s available at all.
Make sure you have an ESTA (or a full visa) sorted out before travel or you will not be able to board the plane.
One other tip. Get an e-sim from someone like Nomad or Airalo. Then you can use that for data. Getting a sim in America never seems to be as simple as it should be.
Pretty sure the scary warnings in big bold text are more recent than this report.