I'd suggest typing man find
and searching for atime, ctime and mtime. I'd also suggest man uptime
and man last
(hint search for -x).
Then I'd search google with something like atime ctime mtime
and have a look at sites like http://www.brandonhutchinson.com/ctime_atime_mtime.html
to see what the terms mean.
Lastly, I'd suggest reading the forum rules about asking for specific help with homework...