first step to customize the header

[Claudio]

I´m trying to match my actual wordpress style into xenforo, so I´m practising how to customize the xenforo header template for example

as I see, its no so easy to insert html code on it..

I have tried to replace the content of header template by:

<h1>This is heading 1</h1>
<h2>This is heading 2</h2>

but I can´t see nothing...how can I make this work and insert html code on any template?