Need Simple help in PHP

<?php session_start(); 
		$logins = array('username' => 'password','' => '');
		$Username = isset($_POST['Username']) ? $_POST['Username'] : '';
		$Password = isset($_POST['Password']) ? $_POST['Password'] : '';
		if (isset($logins[$Username]) && $logins[$Username] == $Password){
		} else {
			$msg="<span style='color:red'>Invalid Login Details</span>";
<!doctype html>
<meta charset="utf-8">
<title>Login to continue</title>
<link href="./css/style.css" rel="stylesheet">
<div id="Frame0">
<form action="" method="post" name="Login_Form">
  <table width="400" border="0" align="center" cellpadding="5" cellspacing="1" class="Table">
    <?php if(isset($msg)){?>
      <td colspan="2" align="center" valign="top"><?php echo $msg;?></td>
    <?php } ?>
      <td colspan="2" align="left" valign="top"><h3>Login</h3><h3><a href=""></h3></td>
      <td align="right" valign="top">Username</td>
      <td><input name="Username" type="text" class="Input"></td>
      <td align="right">Password</td>
      <td><input name="Password" type="password" class="Input"></td>
      <td><input name="Submit" type="submit" value="Login" class="Button3"></td>

i have this simple php login code in which it requires username and password to login that are in array i don’t know much about php i need to use only password and not username can someone please correct it?

Not sure what you are trying to achieve here or how you want to use password without a username, but the data in $_POST is an array of data submitted from your form.