全局$ _SESSION变量

I'm trying to make a login session on PHP, but it appears that the $_SESSION['username'] dies inside the IF sentence (I thought $_SESSION where globals by default), and I cant echo it out of the IF

heres My code

if($name=="admin" && $password=="admin")
{
session_start();
$_SESSION['username'],$_SESSION['sesion'];
$_SESSION['username']=$name;
$_SESSION['sesion']=1;
echo $_SESSION['username'];
echo "<br>";
echo $_SESSION['sesion'];
}
echo "<br>";
echo $_SESSION['username'];

The last echo doesnt print its VALUE, So when I redirect it to another page, the page doesnt take the username value

I'm kind of new in this matter So dont be so harsh on me :P How can I do this??

Move session_start() to the top of the file:

// foo.php
<?php
  session_start();

  //....

  if($name=="admin" && $password=="admin")
  {
    // $_SESSION['username'],$_SESSION['sesion']; // Remove this line
    $_SESSION['username']=$name;
    $_SESSION['sesion']=1;
    echo $_SESSION['username'];
    echo "<br>";
    echo $_SESSION['sesion'];
  }
  echo "<br>";
  echo $_SESSION['username'];

session_start() should be above the if statment. best to put it right below the ?php

When You are using sessions in php You must start it with session_start() in every file/page You want to get or set session values, so just add this line to this file and that file You're redirecting to.