Useful for when you want to carry the yarn rather than cutting and weaving in. I would only use this for two or four rows not more than that.
Knit the first stitch with your new colour. (below)
Look at the back of your work to see the two colours side by side. (below)
Bring your previous coloured yarn over the working yarn at the back of your work. (below)
Knit the next stitch with your new yarn and see how the first yarn is trapped behind the second stitch. (below)
Do this loosely so your edge not too tight.