Its all in the man pages
-r = recursive (copy all directories, contents and their subdirectories)
-u = update (if a file/folder exists, do not overwrite unless newer)
-v = be verbose (so when testing in a terminal you can see what is being moved/etc)
--delete = delete files/folders from /destination that are not on /source (so /destination is an exact mirror of /source)
As said previously, you can add the -n switch to preform a "dry-run", and if you have the -v switch on, you can redirect the output to a file so you can see exactly what would be copied/deleted/etc.
rsync -ruvn --delete /source /destination > rsync-dry-run-file-list