The goal of MINES is to walk from the upper left corner
(where you start) to the lower right corner (where the dollar
sign is) without blowing your ass off.

You use the numeric keypad to move in one of the eight
directions from wherever you're standing. When you step on a
square, you'll be told how many of the surrounding squares
contain mines.

If you hit "M" before hitting a direction key, instead of
stepping on the indicated square, you'll "Mark" it -- presumably
indicating that you think there's a mine there. Hitting "R"
before hitting a direction key lets you erase a mark.