[Requesting] Learning HTML Semantics

Looking for someone to give me some tips/resources on how I can figure out html semantics or layouts of a website.

Trying to section off my website design but it's not working with div/sectional id's.
What im looking for: Someone to help me put working section id's or whatever it's called and connect it to main.css soo I can just update main.css and design it easily.

I'll pay a buck 50 or none. Offer me.

Willing to pay someone to give me an example/tell me how to do this also or fix up my code. Also paying someone who could give me a good prime example of pure backend designing for html and css.
Add me on discord. 66#6669

Here's the code:

Spoiler: CODE

index.html

<!doctype html>
<html>
    <head>
        <title>TEST</title>

        <link rel="stylesheet" type="text/css" href="main.css">
    </head>
    <body>
    <br>
    <div id="header"
    <header>
    <br>

    <br>
         <br>
     <br>
    </header>
    </div>
    <div id="container">
     <center>
     <p>_________________________________</p>
     <p><marquee>TEST</marquee></p>
     <p>_________________________________</p>
     </center>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
           <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
           <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
          <br>
     <br>
     <center>
     <p>
      <a href="https://www.sythe.org">
      <img src="https://i.imgur.com/Vj92zmw.gif" alt="Zyric's Banner" align="middle">
      </a>
        </P>
      </center>
    </div>
    </body>
    <body>
    <div id="bottomcontact">
     <p align="middle"> *TEST Discord *Contact us *FAQ
         <br>*Terms of Service
     </p>
    </body>
</html>

main.css

body {
    background-color: Gray;
    font-family: arial;
    color: white;
}

#container{
    background-color: black;
    width: 1150px;
    margin: 0 auto;
    border: solid 1;

#header{
    background-color: BLACK;
}

#bottomcontact{
    background-color: gray;
    width: 300px;
    margin: 0 auto;
    border: solid 1;


}