Since there are 6 total possibilities, that is our denominator.
Since there are 3 numbers you need to get (1, 2, or 3), that is our numerator.
The answer is 3/6 (which can be simplified to 1/2) :)
Hopefully this helps! If you have any more questions or don't understand, feel free to DM me, and I'll get back to you ASAP! :)