You don't. MathElf tutors are only given log ins after they've been selected. For your skills assessment, you'll receive an email with a set of problems and instructions on how to record explanations and share them with our team.
We recommend using the free iPad app ShowMe to record your explanations of the problems you choose. You won't need to log in for that. Just download ShowMe to your iPad, record your videos there, and share them with firstname.lastname@example.org.