session简单一例

login.php

form action="checklogin.php" method="post" name="form1">
p>用户名：input type="text" name="username" size="20" />/p>
p>密码：input type="password" name="password" size="20" />/p>
p>密码：input type="submit" name="submit" value="确定"/>/p>
/form>

checklogin.php

?php
$conn = @mysql_connect("localhost","root","")
or die("数据库服务器连接失败！");
@mysql_select_db("test",$conn)
or die("数据库不存在或不可用");
//获取用户输入的信息
$username = $_POST['username'];
$password = $_POST['password'];
$query = @mysql_query("SELECT username,password,userflag FROM user "
."WHERE username = '$username' AND password = '$password' ");
if ($rows = mysql_fetch_array($query)) {
    session_start();
    if ($rows['userflag'] == 1 or $rows['userflag'] == 0 ) {
        $_SESSION['username'] = $rows['username'];
        $_SESSION['password'] = $rows['password'];
        $_SESSION['userflag'] = $rows['userflag'];
        echo "欢迎登录，点此进入";
    } else {
     echo "用户权限信息不够！";
    }
} else {
  echo "用户或密码错误";
}
?>

main.php

?php
session_start();
if (isset($_SESSION['username'])) {
    if ($_SESSION['userflag'] == 1){
        echo "欢迎管理员".$_SESSION['username']."登录系统";
    } else{
        echo "欢迎用户".$_SESSION['username']."登录系统";
    }
} else {
    echo "权限不够，无法访问本页！";
}
?>