Participants do not need an account/login to join a moderated study. Once they have gone through the System Check you will see the participant in the waiting room.

UPDATED GIF NEEDED

When Moderator is ready, they select a test participant from the dropdown list, then click the blue Start Session button.

They will then join the session as the participant and you will see them on your screen.

Note to start the screen-share make sure to start the recording!