use of の in this sentence


I still have some trouble with the の particle sometimes.

I'm doing my Bunpro reviews rn and he translation gives me sth like "the one
that..."

I didn't quite understand the exact concept behind this particular case
though.

Thanks for reading.

[![my review on
Bunpro](https://i.stack.imgur.com/xd0Sl.png)](https://i.stack.imgur.com/xd0Sl.png)

