How to enter username in form and then search in database to produce if else statement

How would I get the $UN Variable to be set by the input provided by the form. Then use the variable to search in the database to provide a users details. After I would like to compare the encrypted password AND the username to the database to grant access.

I have already been able to get the program to work with providing a username and have the encrypted password show as being correct or incorrect depending on the user input. I have tried different variables and also using different methods of addressing and calling the data such as '' instead of "" but nothing seems to work.

```    <form method="post">
un:
<br><input type="text" placeholder="Enter username" name = "username"><br><br>
pword: 
<br><input type="text" placeholder="Enter Password" name = "password"><br><br>
<input type ="submit" name = "submit">
</form>

<?php
mysql_connect('localhost',"root","usbw");
@mysql_select_db("Login") or die("unable to select database");
$UN = $_POST['un'];
$query = 'SELECT * FROM users WHERE username = "$UN"';
$result = mysql_query($query= 'SELECT * FROM users WHERE username= "dday"');
$user_info = mysql_fetch_assoc($result);
$temp = md5($_POST['password']);


if (isset($_POST['password'])) {

echo $user_info['pword'];
echo "<br>";


if($user_info['pword'] == $temp AND $user_info['username'] == $UN) {
    echo "You have logged in. <br>" ;
}
else {
    echo "'" . $_POST['password']  . "'"  . " is the incorrect password. <br>";
}
echo "your password is:" . $_POST['password'] . "<br>";
echo "your encrypted password is :" . $temp;
}
mysql_close();

?>
```

I expect if I enter the un as 'dday' and pword as password to log me in otherwise it will say the password you entered was incorrect