Finding actions for blocks?

I'm pretty lost with the (quite frankly very terrible) documentation for scripting. I need to know how to find the available actions for a block, but I cannot seem to find help anywhere on the internet or these forums for this issue. For instance, you can open doors with something like...
IMyDoor Door = (IMyDoor)GridTerminalSystem.GetBlockWithName("MyDoor");
Door.GetActionWithName("Open_Off").Apply(Door);

I'm lost though. How did the person who originally wrote this code know where to...

Finding actions for blocks?