Stuck in a pattern

[supersue]

I am knitting a sweater, my pattern says to knit across 15 stitches, slip 6 onto a holder which I have done, the next part says to join a second ball of yarn and knit across remaining stitches. Working both sides at once with separate balls of yarn bind off 2 sts at each neck edge.

I am not sure how to join the second ball of yarn and what the rest means.

Can anyone help?????

[suzeeq]

Joining yarn is just leaving a tail and starting knitting with the new strand. To do this part, k15, drop the yarn, put 6 sts on the holder, take the new yarn and knit to the end of the row. ** Next row, work back over the 2nd set of sts, drop the yarn, pick up the y