Using your left needle, insert from top to bottom underneath all 4 floats from previous 4 rows of slipping stitches.
Pull the four floats back slightly to reveal the next stitch ready to be knitted. This is the stitch you will be knitting next - see photo 3.
Carefully pull the yarn through the next stitch. This will take some finesse until you get the hang of it. If you're not sure if you've caught all the floats, just pull your right needle out of the stitch and revert to photo 3.
Slide all floats and the newly knitted stitch off the left hand needle.