You have the three letters “A”, “B” and “C”, and you wonder how many different words you can make with these if you can only use each letter exactly once. Since you make a word by ordering the letters, there are different words.
Another way of thinking is as follows: The first letter can be chosen in three different ways, because there are three letters. After you have chosen the first letter, there are two left, so the second letter can be chosen in two ways. When you have chosen the second letter, there is only one letter left, so you only have one choice for the last letter. To get the number of possible “end results”, you multiply the number of choices in each step, and you get .
If you’re in doubt, you can try doing it with pen and paper and see that it’s actually correct that there are precisely six words: