To share an agenda to the administrator, and ultimately, other users, open up the Agendas section by tapping on the second button on the sidebar (highlighted in blue).
To select the agenda in Tablet mode: Hold and slightly pull down.
To select the agenda with a keyboard/mouse: Right click
The option to share will now show on the top toolbar. Tap Share.
A pop up will appear confirming that you wish to share this Agenda with all users, then there will be a notification that the Agenda sharing request has been brought to the attention of the administrator.
If you are the administrator, you can now follow these steps: Sharing Agendas in Media Manager.