Inserting data into MySQL using PHP requires two sets of code, an HTML form and PHP to process the data.  Following is the minimal HTML needed.

<form action='insert.php' method='post'>
  <input type='text' name='data1'>
  <input type='submit'>
</form>

Notice the HTML form action is insert.php. We need to create a file named insert.php.  Following is the minimal PHP needed to insert the data into MySQL.  Notice also that the HTML form method='post'.  When the method is post, the PHP must then use $_POST.  The other option would be to use method='get' and then to use $_GET in the PHP.  Notice also that the HTML input name='data1'.  This needs to map to ['data1'] in the PHP.  

<?php 
$con = new mysqli('ip_or_domain','username','password','database');
$insert = "insert into tablename (columnname) values ('$_POST['data1']')"; 
$processing = $con->query($insert); 
$con->close(); 
?>