If you spin your own yarn, you might have a need to make a ball of yarn into a hank for dyeing or other purposes, and if you recycle yarn from an old project or a thrift store sweater you'll likely want to turn your balls of salvaged yarn into hanks so that you can give them a wash to relax the fibers.
(Of course you can always move directly from ripping out the sweater or project to winding the yarn into a hank and skip the ball stage entirely. Use either method shown here.)
The first part of this tutorial shows how to wind yarn from a ball into a hank using the back of a chair to assist you; the second part shows the same basic procedure done with a yarn swift. This is handy if you have one, but not really that much faster.
To start winding a ball of yarn into a hank on a chair back, take the end of the yarn and loosely tie it to the chair. If your chair doesn't have slats, you could tape it instead.