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 yarn on the other side of the held sts, BO 2 and finish the row. Turn and work the first side, drop the yarn, pick up the other yarn, BO 2 and work to the end of the row. Repeat from the ** and go on to whatever it says next.