The number 1 is neither prime nor composite, so it is not included in either list.
List the factors of the numbers you're comparing. Write down the numbers that appear on both lists. Those are the common factors.
There are infinitely many composite numbers so a list is impossible. Furthermore, there is no systematic pattern to composite numbers so that it is not possible to give a functional definition either. There are, however, some lists of prime numbers and you can remove these from integers greater than 1 to arrive at partial lists of composite numbers. For composites up to 1 million, see the related link.
Both of those lists are infinitely long.
Select two numbers. List their factors. Write down the numbers that appear on both lists. Choose the largest one. That's the GCF.
"Common" means " belonging to two or more quantities." List the factors of the numbers you are comparing. The common factors appear on all the lists.
1 is the factor that is common to all numbers.
All numbers have factors. Some numbers have some of the same factors as other numbers. These are known as common factors. Write out the lists of factors of the numbers you want to compare. The numbers that appear on both lists are the common factors.
All numbers have factors. Some factors appear on the lists of more than one number. These are common factors. 1,2,3,6 1,2,4,8 1 and 2 are common factors of 6 and 8.
The greatest common factor of two numbers has to show up on the lists of factors of both numbers.
List the factors of each of the numbers in the set. Write down the numbers that appear on all the lists. Choose the largest one.
There are around 3,500 such numbers and this site is not suitable for listing them all. You may wish to look at the related link which lists all the primes instead.
The lists of factors of 126 and multiples of 12 do not have any numbers in common.