In this example, I try to explain the Newgrounds API

connect.php

<?php

$sql_username = "root";
$sql_password = "TOMFULPRULEZ1"; 
// For NG's sake, I hope this isn't actually their root sql password. It would be hilarious, though

$database = "Newgrounds Gateway";

$db = mysqli_connect($sql_username, $sql_password, $database);

?>

NG_API_example.php

<?php

include('connect.php');
session_start();

// Note: this is pseudo-code since I don't have a reference handy right now. Don't actually try to use it
// I mean that the functions used here are likely to be fictionally named alternatives to the real function
// for example, exist() is not used to check $_POST's existence, it might not even be an existing function

if(exist($_POST)){ 
  if($_POST['type'] == 'api_connect'){
    $apiid = $_POST['api_id'];
    $enckey = $_POST['enc_key'];
    $result = $db->query("SELECT * FROM api WHERE apiid='$apiid' AND enckey='$enckey'");
    if($result){
      $arr = $db->fetch_array($result);
      $_SESSION['user_api_id'] = $arr['u_api_id'];
    }
  } else if($_POST['type'] == 'api_medal_unlock'){
    if($_SESSION['user_api_id']){ // if this exists, then there has been a successful connection
      $mname = $_POST['medal_name'];
      $u_api_id = $_SESSION['user_api_id'];
      $result = $db->query("SELECT * FROM medals WHERE medal_name='$mname' AND u_api_id='$u_api_id'");
      if($result){ // medal that is owned by user exists
        $db->query("UPDATE medals SET(unlocked='1') WHERE medal_name='$mname' AND u_api_id='$u_api_id'");
      }else{
        die("Error: no medal with that name exists");
      }
    }else{
      die("Error: not connected to API");
    }
  }
}
?>