Click your Username to view the dropdown, then click on Collection. The Green button you're looking for will be at the top-left.
EDIT: The green Add/Update button at the top-right shows up once you click into one of your collections. If you confirm that you're seeing "Add/Update" when viewing your list of collections (and are not within one), contact Admin.
"You don't have to be friends with everybody. Hell, you don't even have to like anybody. But you WILL respect everybody." - My father said this to me when I was 15 years old. It worked. I encourage all of the fathers out there to do the same with their kids.