In earlier versions of Moodle, it was possible for Teachers to log in as individual students. This is no longer possible in Moodle.
Given that anything Teachers do when logged in as a student is recorded as having been done by them, this was potentially problematic and unethical.
Instead, you are able to switch your role in any Moodle course to that of a student, which will replicate what any student on the course sees.
To do this,
This will open the list of roles that you can assume within the course (as above)
To switch back to your normal role,