Welcome to KH!
For most of these patterns you work across the first section, bind off for leg one, work across the middle, bind off for leg two and final work across the last section. You end with 3 sets of sts on the needle. When you turn to the WS, you can work across that last section but then you come to a gap. This is where you need a new end of yarn or a new ball. Attach the new strand to the middle section leaving about a 6" tail and work across to the next gap. Again you’ll need a new end of yarn. Attach that to the last section and work across to the end of row.
When you turn to the RS, you’ll have 3 sections of sts, each with it’s own strand of yarn. Continue working back and forth, knitting each section with its own strand of yarn for 1 1/2 inches.