Functions that are flagged as "optional" within the application might not be enabled within the application you are using. Helpdesk will be happy to enable these functions for you when necessary.
In order to manage and create users, the tab "Administration" (optional) must be enabled for you within the application.
Not every user should be granted access rights to all areas of the application for security reasons. This is why user management gives you the option of only assigning the user those site access rights that the user actually needs. Furthermore, you can create users and view the user log for every user. The user log allows you to view the activities of every user in the application.