You've used up all the free space. Go ahead and click on Install Now.
As the install proceeds, you’ll see a map and the opportunity to update your location. Do so. Hit Forward.
On the next screen, choose your Keyboard layout. The default will be USA, but you change it if that's incorrect. Click Forward.
Now just fill out page asking: Who are you? This will establish your login credentials and other information. Fill out the fields. Click Forward.
At this point, the installer will go on its merry way. It will takes 20 to 30 minutes to complete, possibly more if you're on a slow connection and chose to download third party files during the process. Try to be patient.
After the install process is complete, click Restart Now, and prepare yourself for some major Ubuntu goodness.
Eject your install disc and hit Enter before the restart completes.
With the restart complete, you'll finally see your login screen. Select your username, enter your password, and log into your fresh, new system.
Now your fresh installation of Ubuntu is ready to go! If you want to verify the install, just create a file on your drive and repeat the install process again. This will verify that you can install Ubuntu over the top of an existing Ubuntu installation, keeping your /home directory files intact.
Congratulations. That wasn't so bad, was it?