Step 9 of tutorial doesn't work

Hi there, I´m learning how to use Jekyll, and going thru the step by step tutorial.
All steps went well, but in step 9 (collections https://jekyllrb.com/docs/step-by-step/09-collections/) I have a problem. I did exactly what is said, but nothing happens (except that it creates a staff page in the navigation).

Here is my site’s folder: https://www.dropbox.com/sh/yxnul3iyme1lqkn/AACpqcLp4GvLkBZLYgu2twmHa?dl=0

Any advice for fixing it? Thank you so much in advance.