Example of a Simple Button Tile That Runs an Action?

I’m really enjoying SmartThings and am impressed by the huge number of things that it can do, but when it comes to doing simple UI things I’m completely confused.
I can call functions by the triggering of all kinds of sensors and switches, but how can I make a simple button in my device handler that triggers a function by name when it’s pressed?

Thanks for any help!
Is there some page in the documentation that I’ve missed that explains this sort of stuff other than the Tiles page?!