The app works on Chrome browser. It requires additional chrome extension to which you will be prompted after you install the app.
You must be organization admin to list and edit users.
If you are organization admin, the “manage users” page will be accessible from the top menu as below. Then users are listed in a sortable table. You can sort users by clicking the table header. You can filter the user by site access, last activity time. You can also filter user name and email by typing into “Contains text“ field.
Even I installed the chrome extension, the popup says “helper chrome extension“ is needed.
Possible reason: Your chrome is being managed by your company and the chrome policy applied by your company might not allow the required chrome extension to work. Please see the attached screenshot which is from a managed chrome and check that is not the case in your chrome.