To find the factors of a number, we can look for factors to divide it by subsequently.
It is easier to start with lower factors.
Let's start by "2".
Since "54" is even, it is divisable by "2":

So "2" is one of the factors.
Now, we have got 27. It is not even anymore, but it is divisable by "3":

So "3" is another factor.
Now we have got "9" and it is also divisable by "3":

So there is another "3" factor.
And since we have got now another "3", we know it is divisable by "3":

Now we have got to "1", so we found all the prime factors:

Now,, we need to combine them to find all possible combinations.
We will start from low to high.
"1" is always a factor.
There is "2" there, so it is also a factor.
Then we have "3" as another factor.
There is no need to combine "1" with another factor, so we will start b combining 2 and 3:

So, "6" is another factor.
We can combine 3 with 3:

"9" is another factor.
Now we start combining three of them:

So, "18" and "27" are factors.
And now we combine 4 of them, but this is get us back to "54" which is the last factor.
So, the factors of 54 are: 1, 2, 3, 6, 9, 18, 27, 54.