Do you mean the working yarn is on the other end? If so you just need to work on the other side of your knitting.
If you're using circular needles slide the stitches to the other end and turn your work.
If you're using straight needles you just transfer them to the other needle and turn your work. You transfer by sticking your needle straight into the stitches and slipping them to the other needle.
Watch for twisted stitches, too. They will look like the back leg of the stitch is further to the right when the row is stretched. If they are don't panic. You can lift the stitch off with the right needle and turn it around OR the easiest way is knit into the back of the stitch. It's called Ktbl and there is a video. Go to the glossary linked above.
If you mean something else just ask.