Leg opening on dog sweater

I’m really confuse on this pattern I’m stuck on row 2 I with the second yarn and third yarn I just don’t get it

These are the instructions for the leg opening. On row 1 you knit sts then bound off for leg one. You proceeded to knit more sts with a second ball of yarn and again bind off sts for leg 2. Then the rest of the sts were knit.
For the smallest size you have 5sts on each outer section and 30sts in the center section which is between the legs.
For row 2 you’re going to deepen those 3 sections with two gaps which are the leg openings. Rows 2 and 3 are repeated to make these leg openings then in the Closing Row you’ll cast on sts over the bound off sts to close up the leg openings. From there you can knit with one ball of yarn.

Hello

Because you have bound off 2 sets of stitches mid row, there are now 3 section of fabric. You will work each section with a different ball of yarn to maintain the opening that were made by the binding off.

Work the first stitches wih the ball that is already attached. When you get tothe gap where the bound off stitches are drop that yarn and leave it there, skip the bound off stitches.

Use a new ball of yarn for the centre panel stitches until you get to the ext ap here you bound off stitches, drop the yarn, skip the bound off stitches.

Use a new ball for the third section. When you get tothe end of the row turn and continue with this yarn for this section of stitches.

Continue for the number of rows needed. Then you will cast on new stitches to work across the gaps.

I hope this helps.