Sharing secrets requires 'handshake' between the administrator and individual users. All you need to do is to click the 'Initiate Sharing' button available in "Settings" >> "Share Secrets" page. Everything else is automatically taken care of. (Since this happens to be a mandatory configuration, Zoho Vault prompts you to do this when you start using the product).
Until both the processes (initiate sharing and getting approval) are completed, users cannot share secrets with others and vice-versa.
If you are an administrator, you can approve sharing requests from other users or new administrators. In the Zoho Vault GUI, navigate to Settings >> Sharing Secrets and click the "Approve Requests" tab in the GUI.
Please note that the sharing GUI lists only the users who have initiated handshake and the administrator has duly approved sharing. If you do not find any of the users in the list above, it means that either the user has not initiated handshake or the administrator approval is pending.