ls -lh should list files in human readable long format (depending on your shell).
Now, you want to
grep (that's a filter program) for the ones that match what you're looking for.
For example, to find all the files that say david and that were made in 2011, I could use:
ls -lh | grep "david" | grep "2011"
(Yes, there are faster, easier ways to do this, but the idea is to be simplistic for the asker).
In your case, you want to filter both that first block of text for the readable bit being set and the date being in September. Take a look at the output from
ls -lh and you should be able to make your own grep command that works.