Your Glean Dashboard is where you'll see all your users listed.
By default you'll only see your current active users and waiting invites, but you can tick the 'Show Expired' check box to see all users on your account.
From the Dashboard you can:
View and Manage other Admins
Manage user access
Manage Expired users
View Status History
The Last Active column shows when the user last accessed a Glean Event, either by opening an existing Event or creating a new Event.
Note that the Last Active Column will only update if the user was on-line while using Glean.