It's not often you need to wind a ball of yarn into a skein since you usually go the other way around, but this trick is helpful when recycling yarn.
How to Wind a Center Pull Ball by Hand
How to wind a skein of yarn by hand - without getting it tangled - YAK
Winding a Skein into a Ball - Purl Soho
How to Wind a Ball of Yarn Into a Skein or Hank
Knitting Basics: How to Wind a Ball of Yarn
Niddy Noddy Guide - How to Make a Hank and Measure Yarn - AB Crafty
Wind a Perfect Yarn Cake By Hand - One Dog Woof
How to Wind Yarn from a Hank - Stitches n Scraps
What is a Skein of Yarn & What's the Difference Between a Skein, a
How to Wind a Skein of Yarn
Yarn Ball Winding Cost per Skein/Hank MUST Purchase Yarn with This
What is a skein of yarn & the differences between hanks and balls.
How to Hand-Wind Yarn Into a Ball, Hank, or Skein
Winding a Skein into a Ball - Purl Soho