As a project administrator you can control who has access to your project (display tickets, etc.) as well restrict specified acciviti for particular team members. It is possible to grant permission to display and create tickets while not allowing to remove it.
There are two sections (see picture below) in project settings dedicated to manage project permissions and roles.

Below are saome basic information about where permissions and roles management is placed in project settings. For more detailed description, please refer to

Adding user to existing project role

In order to add  particular user to one of existing project role, go to Users and roles section and select an option  Add users to a role.Then find user and assign role

Permissions assigment review

To determine what permissions are assigned to which project role, go to Permissions section. Here you can see what permission scheme is currently assigned to your project.