How do I print 4x6 photos from photos on my Mac to my printer

If you are using Photos on a Mac (you give zero detail about what you have or why you are asking) then select the photo, click on 4x6 and print - very simple and straight forward

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1 - crop the photos to the 4 x 6 aspect ratio.

2 - with the photo(s) selected type Command + P to start the print process.

3 - in the Print window select the printer and 4 x 6 borderless paper size.

4 - select the 4 x 6 layout option.

5 - print.