Most projects require more than one skein of yarn. It is best to add new yarn at the beginning of a row so the joining is not visible in the middle of a piece of work.
1. To join yarn at the beginning of a row, simply drop the old yarn and pick up the new yarn and continue knitting using the new yarn.
2. Begin knitting, by picking up a new stitch, as normally. But do not wrap the the right needle with the current yarn. Instead, take the first 12 inches of your new skein (the 12 inches is simply the tail, you will sew into your work at the of your project) and simply drape a very small piece of yarn over the waiting stitch (the same stitch currently being held by both the right and left needles). Then continue the knit stitch as you would normally.
Basically, as you knit, there will be a 12 inch tail or a tad bit more of yarn from each of your new skeins of yarn. Those tails should be tied to the previous skeins' tail -- and, at the end of your project, use a needle made specially for yarn to sew the tail into your work.
3. After you have worked a few rows, twist the ends around each other and weave them into the
edges in opposite directions on the wrong side.
The video, below, has been added for your convience, as a visual aid or sorts... if you have any questions -- do not hesitate in contacting me (email, text, call or skype).
Russian joining: This is another option in joining the old and new skeins of yarn in your knit and crochet project. Please note, this make take many practices in getting this technique just right.
And, do not be concerned if the option abovet is easier... there is a way in which to knit the tail into your work, if you use the option above. I will be happy to show you in class. Just let me know, if you would like further information.
The option below, maybe more intriguing for far advanced knitters and crochetters.