portforwardpodcast's answer isn't very well-suited for your purposes, here's a process for you to ponder
Server accesses the following page: heartbeat.php?port=25565&maxplayers=25&players=2&name=Cheese_Pizza_Palace
Your PHP script will then do the following...
- Go through each value, making sure they're all the types you want them to be (integers/strings)
- Connect to the database
- Update the server in the database if it already exists, create it if it doesn't
- Return some value so the server knows that it completed successfully.
And to display the servers
- Fetch all 'active' servers
- Loop through them and display each one.
Things you'll need to figure out:
- How to determine uptime
- How to determine "active" servers
- How to update/create MySQL entries
- How to (properly) connect to a database. I would suggest using PDO since you're using PHP. It's a bit difficult to learn, but it's much more secure than writing the queries directly.
- How to loop through all the GET variables.
Good hunting!