There are 6 outcomes for each die of the pair.
So, there are 6*6 or 36 possible outcomes when tossing a pair of dice.
Let one die be red. Let the other one be green.
To get a sum of 2 when tossing the pair of dice, you must get a "one" on the red die and a "one" on the green die because the sum of those two results is 1 + 1 = 2.
There is exactly one way to get a sum of two when you toss the pair of dice. There are 36 possible outcomes.
The probability of (sum of 2) is 1 / 36.