$n$ choose $k$, $n!$, bars and stars method are all different methods you use to get the result your looking for when it comes to counting problems, my question is when do you know when to use what.
i.e. $n!$ is used when there are no replacements allowed $n(n-1)(n-2)\dots$
$n$ choose $k$ is used when you need to choose $k$ subsets out of set $n$
but when do you use the bars and stars method?
are there any context clues or something i need to look out for when reading a problem, that can help me determine when i need to use the bars and stars method or the other methods