Using custom fonts in my website

If I'm using a font like Geosans Light in my website do I need to add the CSS and files before writing any other code because whatever I try it doesn't seem to work.

Do I add the...

  1. @font-face {
  2. font-family: GeosansLight;
  3. src: url(GeosansLight.ttf);
  4. } the reset.css file or style.css? 

I'v tried comparing my css to forum stuff but no matter what I try my fonts won't change when I view it in my web browser. Someone please help. 

Thanks, Matt 

You can add it to style.css, if that is your main style sheet, or you can put it directly into the HTML.