to give you a basic example -
you would need to have a database with 1 table, lets call it people_events.
people_events would hold several columns, the basics could be -
id | fname | lname | event_name | attending
an example entry -
1 | John | Smith | Jane's birthday | No
When you send an invite, your link could look something like -
http://www.mywebsite.com/events.php?id=1
Now you would use PHP to fetch the id from the URL and search the database for that id -
PHP Code:
$person_id = (int)$_GET['id'];
$query = "SELECT fname, lname, event_name, attending FROM people_events WHERE id = $person_id LIMIT 1";
Use HTML to build your form, they choose whether they are attending or not form a drop down, form gets submitted, PHP updates the database for that user id.....simples
