Below are the 36 possibilities (the *'s) of the upfaces on the roll of two 6-sided dice. Read the points as (Die 1, Die 2). Note that the 7's (sum of upfaces 7) fall along the main diagonal starting with the point (1,6) and ending with the point (6,1).
 
        6 -     *         *         *         *         *         *
  Die 2   -
          -
        5 -     *         *         *         *         *         *
          +
          -
          -
        4 -     *         *         *         *         *         *
          -
          +
        3 -     *         *         *         *         *         *
          -
          -
        2 -     *         *         *         *         *         *
          +
          -
        1 -     *         *         *         *         *         *
            ----+---------+---------+---------+---------+---------+--Die 1 
                1         2         3         4         5         6