Install the Copy App
Once you sign up you will be able to sign into your account. At the top you will see a grayish bar that has some good information. On the top-left of the bar you will be able to click on "Install App" and that will download the Copy App to your computer. Follow the onscreen instructions to get it installed. You should be able to take all of the default settings.
You will also notice on the right side of the bar the amount of storage you have. Once your done installing the app you should check your email so you can confirm your account and then you should receive an extra 5GB from using this toolset. This should put you at 20GB.