In programming, multiple threads can communicate with each other by signaling events and handling events. An event, then, is like a message from one thread to another. In Scratch, blocks whose labels begin with "broadcast" signal events whereas blocks whose labels begin with "when" handle events, the latter of which, recall, effectively represent threads themselves.

This tutorial introduces budding computer scientists to the building blocks of programming by way of Scratch. It assumes that you are already familiar with Scratch's usage and, accordingly, have a general sense of how to program with Scratch. This tutorial aspires to formalize your understanding of programming, framing some basic programming constructs in the language of Scratch. After all, it is either true that some number is less than another number or it is false. Sometimes, you want one or more statements to be executed multiple times in a row. To implement this behavior, we turn our attention to loops. But of statements, Boolean expressions, conditions, loops, variables, threads, and events can you construct interesting (and fun) programs. In fact, let's explore the inner workings of what, on first glance, appears to be a very complex program but, ultimately, is just an application of these building blocks.