Confused

Hi ladies, I’ve got a question regarding a pattern out of a book. It’s for a dog sweater. I understand everything else, but before I start this I wanted to clarify.

It’s for the leg openings. The pattern has a note attached. (NOTE all three sections of the Leg Openings are worked at the same time, using separate yarn for each section)???

I new at this and for the most part I try not to ask question, google is amazing LOL! But.

I have no clue what this means? How do I use separate yarn for each section?

Thanks in advance, I know this is probably something easily explained, but I don’t get it at all.