Instructors control who gains access to the materials and data in the course.
You can invite other instructors to join your course under Settings > Access; all instructors in a course have full access to course materials and student data.
How students enroll in the course depends on whether you have integrated Perusall with your LMS or are using it standalone.
Integrated with LMS
Anyone in your LMS course can click on the Perusall link to launch into your Perusall course. Perusall uses the user role provided by the LMS to determine the level of access given to the user in your Perusall course.
To get students enrolled in your course, give them your course code (of the form YOURLASTNAME-XXXX), which can be found under Settings > Access.