How can I use the blockchain API?
Actually, the BlochChain API is pretty good and Ben Reeves has done a nice work implementing it. And for the most part, for free. You only have to know how to send HTTP requests from your code, and parse the Json your app receives. If you think his API is not complete or unworking, do it yourself and make him competition ;-)

An API is designed for programmers, not simple users. What do you want to do exactly?