A prime number is a number that can only be divided by 1 and itself without leaving a remainder. A table of prime factors is a chart that shows which numbers are prime numbers, and which numbers can be made from multiplying prime numbers together.
Let's say you wanted to find the prime factors for the number 24. Using the table of prime numbers, you could see that 2, 3, and 4 are all prime numbers. The prime factors of 24 are the first two numbers multiplied together: 2 x 3 = 6, and then 6 multiplied by the third number: 6 x 4 = 24. So the prime factors of 24 are 2, 3, and 4.