Find the GCF of both numerator and denominator and then divide both the denominator and numerator by that and you will get the simplified fraction.
It's a factor. This concept is widely used throughout algebra, and you'll probably bump into it through the end of high school and beyond.
A common use is expressing a term in <em>prime factorization</em>, or reducing a number to its most base parts- primes. For example:

Of course, a number like 13 which is already prime is made up of itself and 1. <em>Factors do not have to be primes.</em> 20 is also reducible through combinations of 1, 2, 4, 5, 10, and 20. Prime factorization is just a handy example.
Basically, factors multiply with each other to create other numbers, and numbers can be reduced down to their factors.
Answer:
5/36
Step-by-step explanation:
Dice 1 cannot be 1 no matter how large dice 2 gets
Dice 1 = 2,3,4,5,6 each matches with dice 2 to get a sum of 8
+/- 13 I believe is the correct answer