To develop an app like this one needs to know right interfaces that iOS Developer library offers to control other apps. Suppose I had this idea, how can I figu

To develop an app like this one needs to know right interfaces that iOS Developer library offers to control other apps. Suppose I had this idea, how can I figure out the correct API reference documentation. I tried it with various keyword searches and I couldn't find it. I find this the case on any other platform - Windows, Android, and OSX. I wonder how others solve this problem - finding the right reference among ton of documentation.