“just show up”
Show up means to appear or attend. Just show up says that coming is enough and no preparation is needed.
A2-34 / CEFR A2 / EPISODE 34
Asking about workplace training
SceneFrank is meeting with a trainer at his new job. The trainer is explaining the schedule and what to bring.

WORDS & CONTEXT
Show up means to appear or attend. Just show up says that coming is enough and no preparation is needed.
You know what? usually introduces an idea or change of topic rather than checking knowledge. Seeing how closely Frank has studied the handbook gives the trainer an idea.
Both means the two of them. The handbook gives the break as both ten minutes and fifteen minutes, so Frank checks which is correct. The line shows that he has read not just all the pages but the small details too.
A new hire is a newly hired employee, and the verb train means to teach or instruct. Maybe you should ... is a way of making a suggestion. Here the trainer, amazed at how much Frank knows, jokes that maybe Frank should take over as the one who teaches. It is not an official assignment for next year.
"You'll be my first trainee." Frank takes the trainer's joke seriously: the person who was teaching becomes a student in Frank's training, and even gets homework to read all 212 pages. The punchline is the reversal of roles; no actual change in who runs the training has been decided.