Do not be fearful of the monks , they are so amiable
Here is a working copy of your code.
First thing to do is read perldoc Class::Struct
Using an editor with color coding can help u catch trival issues in perl like doc as opposed to $doc.
you will also be greatly benefitted by reading perldoc perlreftut to understand how references work.
coming back to perl after many years, i realise the key to understanding a language is through its basic data structures, so perldoc perldata / perldsc and perlvar are your manual until you reach the level of proficiency

package TestPackage;
  2 use strict;
  3 use warnings;
  4 use Class::Struct;              # include <structs>
  5 
  6 struct( document => {
  7     fileID  => '$',             # $ = scalar = int
  8     filename => '@',            # @ = array (of char) = string
  9     tags => '@'                 # tags - array of strings
 10 });
 11 
 12 # all of these three attempts to allocate memory fail:
 13 #my $doc = document->new( );     # produces: Can't locate object m
+ethod "fileID" via package "doc" (perhaps you forgot to load "doc"?) 
+at testsnippet01.    pl line 18.
 14 #my $doc = new( 'document');     # produces: Undefined subroutine 
+&main::new called at testsnippet01.pl line 12.
 15 #my $doc = new( document);       # produces: Bareword "document" n
+ot allowed while "strict subs" in use at testsnippet01.pl line 13.
 16 
 17 my $doc = new document;        # Hopefully a Perl saint knows what
+ goes here...
 18 
 19 $doc->fileID( 123 );
 20 $doc->filename( ['SampleFileName'] );
 21 $doc->tags( ['tag1', 'tag2', 'tag3']  );
 22 
 23 print "File ID:  ", $doc->fileID, "\n";
 24 print "Filename: ", $doc->filename->[0], "\n";
 25 print "Tags:     ", $doc->tags->[0], "\n";
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