I find sessions in php kind of confusing, can anybody of you explain those to me. I have an example which is not working in my case: I register sessions this way, would you please tell me is this the right way of registering sessions

 //this is the page from where i register myusername in sessions
if($count==1){
    session_start();
    $_SESSION['myusername'] = $_POST['myusername']; 
    include("enterpincover.php");
}
else {
    echo "Wrong Pin";
}

here i check first whether the username is registered in sessions in oder to open his account , otherwise open again login.

It works, if user is not loged in, it will show login page which is right, if user is loged it shows welcome message but not the Welcome the name of the user as I want. for ex: Welcome David

<?php
session_start();
if(isset($_SESSION['myusername']))
{
    echo 'Welcome '.$_SESSION['myusername']; 
}
else
{
    include("leftmodules.php");
    include("rightmodules.php");
    include("login.php");
}
?>