An M1 knitting stitch is a way to increase the number of stitches on your knitting row. M1 is an abbreviation for "make 1" stitch. Sometimes the abbreviation also says "inc," for "increase," which also means M1. When you see inc or M1 in your pattern directions, it means that you have to increase in a stitch. It is easy to do this by making two stitches out of one.
Knit the M1 stitch as you usually would, but instead of pulling it off the needle, keep it there.
Take the right needle, and insert it behind the stitch. This is difficult, especially with yarns that have little elasticity. You will have to push on the needle to get it through the back of the stitch.
Wrap the yarn around the right needle, and pull it through, as if you were knitting the front of the stitch.
Take the stitch off the needle. You will now have two stitches made from one.
This is the easiest way to increase without making holes in your knitting. Practice increasing on a sample swatch for a while. It will get easier.