Turning a template into Perl code means turning a template inside out: typical templating systems use a mixture of HTML and Perl (or Perl and "something else", which isn't necessarily HTML), where the Perl is "inside" the HTML. Like this, sort of:

    <b>Name: </b><% $name %><br>
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The HTML is the outer layer, and the Perl is contained within special sections marked off by some delimiters. In this case, <% and %>.

Most templating systems will turn something like the above into this:

    $_out->("<b>Name: </b>");
    $_out->( $name );
    $_out->("<br>");
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Imagine $_out is a subroutine reference that is basically just

    my $_out = sub { print @_ }
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So essentially, "turning a template into Perl code" has created a piece of Perl code with a bunch of print statements, which is what you might have written if you hadn't used templates at all. This is what I mean by turning the template inside out: you have taken a template that was HTML with embedded Perl, and have turned it into a Perl script with embedded HTML.

The advantage to Perl code is that Perl code is fast. :) Ie. if you have a block of Perl code, you can execute it directly; you don't have to parse it as a template. So you can store it in this intermediate Perl script form, and then just run it again without reparsing the original template.

This is a relatively standard way of caching templates for many Perl templating engines. And obviously, this is just a small example, but it shows the basics of how it works.