External members have very limited capabilities in comparison with the academy members. Specifically, they can only view the courses that are public to external members and all of them view the same set of training since they do not have jobs, org nodes’ associations, etc.
The main use of that kind of account is for evaluating people before you hire them. So, you can, for example, add those users in the platform as external members, have them take a test, and if they pass with a certain score, hire them, and convert them to regular members within the academy. So, the goal is usually to have those users initially into the academy temporarily as external members and then, convert them to regular members.
External members have access only to Courses (not Curricula) and can see Lectures, Exams, and Polls but not On The Job Trainings and Events.
They can only self-enroll in courses that are available for them, meaning that you, as an admin, do not have the ability to assign courses to external members.
Please note that the courses that are public for external members need to also belong to the academy course category "Without Category" in order to be visible to them. Youn can learn more on how to make courses public for External Members here: Can corporate courses be visible only to employees and/or external members?