I'm not sure what you're asking, so I'm gonna venture a guess.

@F is only populated when the -a option is used, and -a must be used in conjunction with -n or -p. None of these are particular useful for scripts. If you want to do split a string into columns, remember that
perl -nae '...'
is equivalent to
perl -e 'while (<>) { @F = split(" "); ... }'

Does that help?

Perl command lin switches are documented in perlrun.
split is documented in perlfunc.

PS - When posting code here, put <c>..</c> tags around the code. It makes it more readable, escapes special characters, and allows wrapping.