Customizing the gallery shortcode on a global level

This text is mentioned In the Codex page concerning the gallery shortcode:

You can also print a gallery directly in a template like so:
<?php echo do_shortcode('[gallery option1="value1"]'); ?>

There’s no other information about this. I’m a little confused about customizing galleries. I would rather make changes on a global level, and not have to specify options each time I use the shortcode (in posts), but it’s unclear to me exactly where I would use the code above. Which “template” is this referring to? Is there a dedicated galley template that I don’t know about?

Thanks!