Need help with pattern directions for dog sweater

I’m working on a dog sweater in the Leisure Arts Leaflet 2984, I Can’t Believe I’m Knitting. Am having a problem understanding the instructions for the Leg Opening. There is a special note in a box which says:
All three sections of Leg Openings are worked at the same time, using separate yarn for each section.

Does this mean that I should use yarn wound on two yarn bobbins in addition to my main yarn source (or 3 separate balls or skeins of yarn)?

Is there any tutorial for knitting on the internet that illustrates how to do this?

Beverly

Here’s a video of how to wind a center pull ball. You can make these for your leg holes. No bobbins necessary.