iOS app connect to website

What resources are available for me to learn how to connect my app to a website like Facebook or Angie’s List or Ebay?

Usually webstes like Facebook provide APIs to use their services. Create a developer account ( Facebook Developer Portal) and use the sample code to start.

Facebook was just an example. I actually would like to know what parts of Cocoa Touch to learn to be able to, for example, create a table view with content from a website. How do I point objects in Cocoa Touch to urls?