The technique of pulling the top thread to the underside is exactly the reverse of what you do when you want to pull the bobbin thread to the top of the work. Lower the needle into the fabric and drop the presser foot. Manually turn the balance wheel to bring the needle back to its highest position (you will have looped the two threads together in the first stage of forming a stitch). Lift the presser foot and take your hand underneath the fabric to get hold of the bobbin thread tail. Tug on this bobbin thread to bring a loop of the top thread to the underside and then pull this top thread through to the underneath. And that's all there is to it.
I suggest you only do this when working on a single layer of fabric such as quilt top/cushion top. The thread tails on the underside will be unsightly and so I personally would want to conceal them with additional fabric layers - such as the a lining on a cushion front or the wadding and backing of a quilt.