League Pulses uses the same templating system that MADCAT does. So, if you're familiar with MADCAT's system you're good to go. If not, you just need to be familiar with HTML and CSS.

Modifying the template allows you to define the header, footer, and menu of your site. Modifying the CSS allows you to define the colours and fonts of the site. This gives you a lot of control over the vast majority of your site's visual look and feel.

The internals of the pages cannot be directly changed (though the look of tables can be changed quite a bit via CSS), because you cannot modify the source of the pages.