Board Thread:General Discussion/@comment-66.186.76.49-20130117184618/@comment-4787430-20130117195054

M1 and M2 refer to the left and right buttons on the mouse. M1 = mouse 1, M2 = Mouse 2. I don't know if you are playing it without a mouse, but it should be the same thing. If not, you have an option to change what buttons you use for attacking.