make 1 right leaning increase stitch
M1r simply means to “make 1 right” and is an increase stitch.
Pick up the bar between the last stitch you knit and the one you're about to knit, bringing the needle from the back to the front. Now twist your right needle to the front of this stitch and knit this stitch as you would normally. This will twist your stitch and you won’t be able to see a hole in your work like you would with a yarn over stitch.