Data from API

Hi guys,

This is possibly a very stupid question, but I have never worked with (or needed) to work with an external API to get data on any of my projects.

But after getting some API documents from UKMail (UK currier company) it could prove to be pretty nice and beats scraping the data.

Now, I have no idea where to start with this in CodeIgniter, I have the documentation that tells me what data I need to pass, but have no idea on how to pass that data, as far as I can tell I send some data to the API and get XML data back?

Is there an example anywhere for passing information to an API? I searched around but can only found things to do with REST, is this what I want?

Any help on getting me started would be fantastic.

Cheers,
Neodite