The purpose of the tags program is to bookmark where a variable or sub was declared, so that you can go back to that point when needed.
Say you have this script:

use DBI;
use strict;
my $DNS = shift;
my $dbh = DBI->connect($DNS);
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Save it as test_DBI.pl and then run

$ /your_path_to_it/pltags.pl test_DBI.pl `perldoc -l DBI`
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(perldoc -l returns the path of an installed module).
Then, editing test_DBI.pl, if you have your cursor over the "connect" word, Ctrl-] will take you to the DBI.pm module, at the line where the "connect" sub was defined.
In your case, replace the script and module names and you'll have some more tags available.
HTH

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