Click on a share method to enable it.
If an option is highlighted, then it has been enabled.
To disable a share option that's been enabled, there's a toggle switch in the menu for each share method.
Unique URL is automatically enabled when it is being used in conjunction with one of the share methods.
After you've selected and customized your share options, you'll want to select the share screen layout.
Much like the Start Screen, you can choose from:
And, like the start screen, you can also Create a New Share Screen layout.