i understand that

I just dont understand where you write all this

i dont know where i need to put the check address function

since i have 2 files

1 is the container.php file with this in it

   
    Submit
 

and once clicking submit  it uses the info from the submit.php

which is this file

include_once 'db.php';

$eth = mysqli_real_escape_string($conn,$_POST['address']);


$sql = "INSERT INTO address(address) VALUES('$eth');";
mysqli_query($conn, $sql);



now where do i put the checkAddress function so that i can check if address is valid?