Only "Preview" and "Publish" Buttons are Displayed
This simply means your collection has not been published yet. Simply click the Publish button, on the bottom left of your collection management dashboard, to publish the collection. Once published, you will see the Share button displayed.
If you are only seeing the "View" button, your collection is likely in "Hidden" status.
Only 'View" Button is Displayed
When your collection is "Hidden" it means it is no longer published and is not viewable to your clients.
1) To publish, simply click the green quick edit pencil next to your collection title.
2) Change the status to "Published" in the drop down Status bar.