Let's learn how to close a ball. After crocheting the last circle, leave 20 cm of yarn to close the ball. Thread the yarn with a sewing needle, and insert it through the front loop only of all stitches in the same direction.
The front loop only(flo) is the loop close to us. This is one stitch, and this loop is near us. So this loop is the front loop. The needle through this loop. And through all front loops of all stitches. Then pull the yarn tight. The ball is closed.
Now hide the tail. Insert the needle in the center of where the hole used to be, and out on the other side of the piece. Then the needle is through from the current stitch, find a stitch at random and pierce it out, Repeat 2 or 3 times. Cut the tail as close to the piece as possible. Squeeze the ball, and the yarn tail disappears in the ball.