Simple PHP Login Help..

[Jaquio]

Alright, I have been trying an trying there are a few threads out there from where I have tried to make one. It seemed to work, but it actually didn't.. Anyways, I want to make a simple login/logout script. Using a Functions.php file holding the login an logout functions. While in the other file, has the login page, an the logout. Something kinda like this.

Functions.php

<?php
require("Header.php");

//Logs you into the site.
Function Login($User, $Pass, $MinRank, $mID){
    global $MyRow;

    $result = @mysql_query("SELECT * FROM Members WHERE Username = '$User'");
    $MyRow = mysql_fetch_array($result);

    if($MyRow != Null){
        extract($MyRow);
    }

    if($User == $Username && $Pass == $Password and $Username != NULL){

        if($Rank >= $MinRank){
            return 1;
        } else {
            echo("Logged in!, Rank isn't high enough.");
        }
    } else {

        if($mID == 0){
            echo("<br><center>
                <form action=User_CMD.php method=POST>
                    Username:<input type=username name=Username>
                    <br>
                    Password:<input type=password name=Password>
                    <br>
                    <input type=submit value='Login'>
                </form></center>    
            ");
        } else {
            echo("Not Logged in!, mID != 0");
        }

    }
}

//Logs you out of the site.
Function Logout($User){
       //Place logout stuff here.
    echo("You are now logged out!");
}

?>

An here is the other.

User_CMD.php

<?php

require("Functions.php");

$Action = $_GET["Action"];

if($Action == NULL){
    if(Login($Username, $Password, 0, 0) == 1){
        //Display Profile, Console, Private News an whatever else here.
        echo("<br>
            <center>
                Logged in!
            </center>
            <br>
        ");
    }
}

if($Action == "Logout"){
    if(Login($User, $Pass, 0, 0) == 1){
        Logout($Username);
    }
}

require("Footer.php");

?>

How could I possibly add-in cookies or sessions doesn't matter which ones I use peferably sessions though. Just as long as the user can login an out.