the app doesn't support all the features of Moodle web, we keep adding some of them. We don't support most of the admin options, we focus on supporting student features.
The only way to search users in the site is to go to Messaging > Contacts and search for them, there is no way to browse all the users.
Regarding courses, the only way to view all the courses is by adding the "Available courses" option in the Site Home. Then the app will display that option that allows you to browser all courses, but you won't be able to manage them.