I am wondering if anyone can help explain to me the difference between coding on QuantConnect.com IDE vs using the QuantConnect API?

As I went to look for QuantConnect  tutorials at:


However when you click tutorials link it began talking about the QuantConnect API tutorials only. Is QuantConnect API what I use when writing algorithms in the online IDE? The coding examples seem to be the same as how I code in the online IDE, but we are also given an API key in which I do not use online. 

Anyhting Helps,