Don't leave your homework to the last minute.
Your example doesn't work because you don't run the query, which it seems is done by this code:
$conn = mysqli_connect($host_name, $username, $password, $database)
or die("Could not connect.");
$result = mysqli_query($conn, $sql1)
or die("Could not execute SQL query");
if ($result) {
echo("Data added successfully !!");