The video will be good help, but sometimes it is nice to have it written down as well. If you are on the knit side: When you come to the place you want to do the w/t, keep the yarn in back, slip the next stitch as if to purl, now bring the yarn to the front between the needle tips, then slip the stitch back to the left hand needle. Now you are ready to exchange the needles in your hands so that you are turned to work back in the other direction. Move the yarn to the front if the next stitch is a purl, and start working the next row.
If you are on a purl row, keep the yarn in front and slip the next stitch purlwise, move the yarn to the back between needle tips, slip the slipped stitch back to the LH needle, turn and if the next stitch is a knit move the yarn to the back before knitting.