Components are not just for static markup. A component can have its own controller that enables users to interact with it. This is useful for web functions that occur on multiple screens, such as a search bar that only searches through records of the sObject in the standard controller. It's also useful for web functions that occur multiple times on a single page. A great example is uploading files. Normal behavior on the Salesforce1 Platform is to upload one file at a time. Most people are okay with this, but sometimes when you're uploading a long list of files, you might forget which ones you've already done. You could just use a Visualforce page with a bunch of <apex:inputFile> tags on it, but wouldn't it be so much cooler to perfect your upload user interface in a component and then reuse that component multiple times on the same page? Let's start by creating an Apex class named fileUploaderComponentController:

public with sharing class fileUploaderComponentController...