The generated style.css defines the font face icon-btz.
You can either copy the contents of style.css to your own CSS or link to it in your HTML like so:

<link rel="stylesheet" href="style.css">
<link rel="preload" href="fonts/icon-btz.woff2" as="font" type="font/woff2" crossorigin="anonymous" />

This code assumes style.css is located in the same directory as the HTML file linking to it. The second line is for enabling early font downloads. You may need to adjust the value of href and the URLs used within style.css depending on where you place the generated files in your setup.

Use the CSS class icon-btz to apply the generated font to any text:

<span class="icon-btz"></span>

You could change the size of the glyph using the font-size property in CSS:

.my-size {
    font-size: 2em;
}

<span class="icon-btz my-size"></span>