No, you let the "old" string of yarn hang loose. Then you use the "new" string of yarn from the new skein as you would normally. Just be careful to keep the proper tension otherwise it'll get all wonky. Don't over lap them. I hope that helps! ;)

Hi, Fingersmith!

You can definitely use both of the strings as one to knit several stitches. This serves the same purpose as weaving in the ends. It only works, though, if you're ok with the two strands being used together both in terms of the double-thickness and in terms of the colors.

In other words, you may not want to do this if you're using very thick yarn, or if you're doing something where the two colors together might interrupt a pattern.

However, if you're doing a fairly plain scarf in worsted-weight or thinner, or one where your color changes are interspersed randomly, then it can be a good way to go. Easy to get the hang of it, plus you don't have to worry about those pesky ends :)