Page Layout with menu and pages

Question

i have the follow problem, i have create a page layout like follow

HTML

        <header>
      <?php include('header.php') ?>
    </header>
    <div class="main">
      <nav>
       <?php include('menu.php') ?>
      </nav>
      <div class="content">
        <?php include('main.php') ?>
      </div>
    </div>
    <footer>
      <?php include('footer.php') ?>
    </footer>

CSS

    html, body{
    height: 100%;  
  }
  header{
     height: 20%;
     background: yellow;
  }
  .main{
     height: 70%;
    background: blue;
  }
  footer{
     height: 10%;
    background: yellow;
  }
  nav{
    width: 20%;
    height: 100%;
    float: left;
    background: green;
  }

and in nav i have i vertical-menu you cant find here, now i want something simple of course, when the user click a link from menu on the .main layout show the page i want etc. page 4 and not redirect me to the page 4.I want to work als frames.

I was thinking its page to have the the same header,and nav i don't know if this is right, i don't know if there is a simple way.