Simple Combinatorics Order does matter:  
$$\begin{align*}
&1 2 3\\
&1 3 2\\
&2 1 3\\                       
&2 3 1\\
&3 1 2\\
&3 2 1
\end{align*}$$
Order doesn't matter:
$$1 2 3$$
How does this work? Order doesn't matter: $1 2 3$. Can't it also be say, $3 2 1$? Doesn't this also show that order doesn't matter.           

The number of ways in which 1, 2 and 3 can be arranged whereby order matters can be calculated using the formula $\frac{n!}{(n-r)!}$, where $n$ denotes the number of items that you can choose from, and $r$ denotes the number of items that you are choosing to arrange. This is called a permutation. In this case $n=r=3$, and so 1, 2 and 3 can be arranged in $\frac{3!}{0!}=\frac{(3)(2)(1)}{1}=6$ different ways.
The number of ways in which 1, 2 and 3 can be chosen whereby order does not matter can be calculated using the formula $\frac{n!}{(n-r)!r!}$, where $n$ denotes the number of items that you can choose from, and $r$ denotes the number of items that you are choosing. This is called a combination. In this case, again, $n=r=3$, and so 1, 2 and 3 can be chosen in $\frac{3!}{0!3!}=\frac{(3)(2)(1)}{(1)(3)(2)(1)}=1$ different way, whereby order does not matter.
