On the left side of the screen you will see a listing of package groups. When you expand this list and pick one group, the list of packages in that group will appear in the panel on the right.
To sort packages by size, click on the Size (MB) tab. To sort alphabetically, click on the Package tab.
To select an individual package, click on the check box beside the package name. A check mark in the box means that a package has been selected.
For more information about a specific package, click on the individual package name. The package information will appear at the bottom of the screen.
You can also select or deselect all packages listed within a particular group, by clicking on the Select all in group or Unselect all in group buttons.