Probably the very first thing your instructor will talk to you about, before you’ve even driven a centimetre.
Your cockpit drill is everything you need to check before you drive – things like making sure your seat position is right and adjusting your mirrors. Basically: is everything cool for you to operate the controls safely and comfortably?
You won’t need to go through the whole cockpit drill in your test if you’ve arrived at the test centre in your driving instructor’s car, because everything will be set up.
If you’re doing your driving test in your own car, make sure you’ve been through the cockpit drill before arriving and you have a spare rearview mirror for the examiner. You won’t fail if you don’t have this but it makes a good impression.