How do sites use other people sub domains to run their site through?

Thank you albertleao, you're a star!

I will have a look into that and learn a bit about these wildcards and see what I can do with them.

Thank you, sorry for doubting you (or misunderstanding) previously.

Best wishes,

Paul.

It's fine, glad I could help. I've played around with wildcards but I've never implemented wildcard subdomains in a production environment so please let me know how it goes.

Codeigniter is simply one of the tools you need to learn to be a successful developer. Always add more tools to your coding arsenal!