In my opinion, the best reference work is still the book: Mastering Perl/Tk. Its predecessor, Learning Perl/Tk, coming a close second. Both of these books devote an entire chapter to geometry management.

In my experience, it's best to use the same geometry manager within a Frame; use Frames to embed a different geometry manager. For instance, several Frames may be pack()ed; any of those Frame widgets may contain a set of widgets using a different geometry manager - mixing geometry managers within Frames typically results in tears.

To illustrate further, code like this is generally fine:

my $f1 = $mw->Frame(...)->pack;
my $f2 = $mw->Frame(...)->pack;
my $f3 = $mw->Frame(...)->pack;
,,,
my $b1 = $f2->Button(...)->grid;
my $b2 = $f2->Button(...)->grid;
[download]

While

my $b1 = $f2->Button(...)->pack;
my $b2 = $f2->Button(...)->grid;
[download]

is typically problematical.

The documentation for individual geometry managers is linked from: CPAN - Tk.

Update: I had 7 instances of mismatched brackets: s/{...)/(...)/ - thanks moritz; s/.-/->/; s/=/->/