In the Perl debugger, the "m" command lists the available methods, including following @ISA and showing you XS routines that are not apparent in the *.pm source code.

Update: For your specific question, it appears that the group() method is what you want. However, a user can belong to more than one group. If you can't deal with more than one group, then you might want to just deal with the first group name returned:

my $group= ( $db->group( -user => $user ) )[0];
# or
my( $group )= $db->group( -user => $user );
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    -- Chip Salzenberg, Free-Floating Agent of Chaos

To expand on chip's point, perldoc has the handy '-m' switch which lists the entire module as found by perl in @INC.

$ perldoc -m HTTPD::RealmManager # paged listing follows
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Look at @EXPORT and @EXPORT_OK near the top for names. If your $ENV{'PAGER'} supports searching, you can go directly to the definition you want.
su

After Compline,
Zaxo

     Sometimes you want to call a method when you don't know the
     method name ahead of time.  You can use the arrow form,
     replacing the method name with a simple scalar variable
     containing the method name or a reference to the function.

         $method = $fast ? "findfirst" : "findbest";
         $fred->$method(@args);          # call by name

         if ($coderef = $fred->can($parent . "::findbest")) {
             $self->$coderef(@args);     # call by coderef
         }
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$obj->method(1, 2, 3);         # general case

if ($obj->can('method')) {
    print "Yep, \$obj has a method named 'method'\n";
}

if ($sub = $obj->can('method')) {
    $sub->($obj, 1, 2, 3);     # same effect as general case
}
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Or just do like chip says, and just look. Duh :-)