I hear about people creating the "hank" first from the spool of yarn then making a ball but I don’t really understand how or why that is done. I just make a ball from my spool. Why should you make a hank?
If your yarn is already in a ball, either oblong or round, it is not necessary to make a hank out of it, nor is it necessary if the yarn is coned or on a spool, a ball can be wound directly cones or spools, or simply knit from the cone or spool. However, it may be preferable to rewind any yarn, regardless of how it has been put up in order to check for flaws in the yarn, including undesireable slubs or knots, since these may fall at a point in the knitting where it is difficult to rejoin the yarns when they are removed.
However, some yarn is still put up in circular hanks or skeins that must be held open in some fashion and then wound into balls. Usually knitters use another person to hold the hank, or use a swift, which is a mechanical device to hold it, or simply put the hank around the back or upturned legs of a chair, or around a large bowl or an overturned stockpot, or even their own feet. The reason for this is to prevent the yarn from catching on itself as it is wound and tangling.