Let's take a look at that example code we just ran. Every Ext component we use will start with "Ext" and will most likely be contained within an onReady function that we will cover with more detail in the next chapter.
Ext.onReady(function(){
Ext.Msg.alert('Hello', 'World');
});
Ext has a very human-readable interface. You can almost read it as a sentence—when Ext is ready, it displays a message box in the alert style with Hello for a title and World as the body.
Our alert message starts with Ext.Msg, which is the starting point for all message style windows, and is shorthand for "MessageBox". The alert portion tells Ext exactly which style of message window to use.