I am confused about the preparation of the cherry and swiss chard stuffed pork tenderloin...are these the small 3"round tenderloins and how are th...

Steps 6-8 cover this pretty well. You cut a hole in the center of the tenderloin lengthwise. If you look at the photo, it is pretty clear that it is stuffed in the center of the tenderloin.

Step 8 has very clear wording: "Using your fingers and the wooden spoon handle, stuff as much of the strained cherry and swiss chard mixture into each loin." Just shove the stuffing in and keep pushing it down until the center pocket is filled.

The author's website has an additional photo not offered in the Food52 website that's pretty clear:

http://mycommunaltable.com/tag/pork-tenderloin/

Good luck.

This is a classic method for stuffed meats.