there are 2 ways of doing this
1. with a large knitting needle [like a size 50] or a large size dowel [ a broom handle will do
2. or using your hand
i am discribing the hand method
prepair your yarn.
unwrapping the yarn. draping the looped yarn over a back of a chair can help keep the yarn more stable.
Hand Method
Hold one free end in your hand and drape the long end around your thumb as shown in picture 1.
Make your hand into a gun, and wrap the yarn in a figure 8 around thumb and finger. Continue in this method until you run out of room on your fingers!
Slide the stack of figure 8s off your finger and thumb and pinch together in the middle.
Pinch the yarn stack between finger and thumb, keeping the starting end draped over your thumb. You want to make sure as you wind the ball that this end remains free and accessible!
Start to wrap the yarn around this bunch in a circular motion to form a ball. Keep your thumb pinched into the middle as you wrap.
Continue wrapping the ball of yarn. You will quickly see it begin to resemble a proper ball and it will be easier to understand what youre doing.
I like to keep my thumb stuck into the center of the yarn where I started wrapping so I dont lose the free end.
Then I just wrap and turn, wrap and turn all around the ball until Im out of yarn.
Finally, tuck in the end of the yarn youve been wrapping so it doesnt unravel.
Now you have a center-pull yarn ball. Take the center end that you kept free, and start your knitting from there!