Put simply a quilting Yo-Yo is a circle of fabric gathered in the middle to form a rosette. Then these yo-yo's are placed side by side and whip stitched together. There are many different patterns that can be created using the yo-yo design. Connecting Threads has a good tutorial on the traditional pattern and how to figure the size circle you start with to create your yo-yo.
One project I made was a small yo-yo pillow that I use on my couch during the fall.
I used various green, blue and beige fabrics to create a scrappy look for my pillow.
The yo-yo's measure ~1 3/4"
I have not tried the yo-yo makers that quilt shops sell today but the Connecting Threads site has a video tutorial on the device. I appreciate the traditional art of hand sewing. There is something therapeutic about sitting and sewing that reminds me to slow down. Too many times today we are in such a hurry to finish a project that we miss the joy in the journey.
For a change of pace take the time to explore some traditional patterns and projects and enjoy the journey.