MULTIPLES
If a number is a multiple of another number, it means that it can be made out of adding groups of the other number together.
Examples
12 is a multiple of 4 because 4 + 4 + 4 = 12 (or 4 x 3 = 12)
27 is a multiple of 9 because 9 + 9 + 9 = 27 (or 9 x 3 = 27)
17 is not a multiple of 4 because it cannot be made by adding groups of 4 together.
FACTORS
A factor is a number that divides into another number with no remainder.
In other words every number is divisible by each of its factors.