Hi canister,
As per essellar's reply (and I thought obvious if you had read at least the first link I provided), you need the HTML to inform the browser it uses the CSS template. As mentioned, this is a two step process:
1.) the HTML must link to the CSS in the <head> section, e.g.: <link rel="stylesheet" href="mystyle.css">
2.) the HTML may need to use special classes/ids depending on how that CSS template was designed (not all CSS will apply to the elements globally)
You really need a better background and understanding on how HTML works with CSS and for that you need to do a bit of reading yourself (no one can really help you unless you help yourself to learn more first and then come back with quite specific issues that we might be able to help you with).
Recommend reading through some of those links I previously posted (esp. at least the first one).
Good luck.