The bullion stitch will take place between A and B.
Bring the needle out through A and put the needle through B at a desired length and bring your needle out again on A.
Wind the thread around the needle as shown. The distance of wound thread should be a little longer that the distance between A and B.
Then, hold the wrapped thread with your fingers and pull the needle out completely.
Keep pulling the needle in an upward direction till the wraps lay on the fabric.
Adjust and straighten the wraps if required and put in the needle back through B.