This moodle block allows user enrolment by showing temporary access codes. To make this working a teacher can add the block inside a course. As teacher a temporary access code for a particular role can be created.
To provide other persons the possibility to enter the code before they are already enrolled to the course the block should be added in any context where the user can access it. This could be a course with guest mode, the dashboard, the frontpage or any page that can display a block.