the -k parameter lets you sort based on a key field instead of the first string. To use it to sort a batch of strings that look like this
-rw-rw-r-- 1 user prod 2406912 May 7 05:00 ./backups/daily/BaseClassAO-050708.tar
-rw-rw-r-- 1 user prod 1703424 May 7 05:00 ./backups/daily/BaseClassP-050708.tar
by the file size, use sort like so
sort -n -k5
telling sort to use the 5th field (as delimited by the space character) to sort on.