BEGINNER - creating mesh and mesh filter

Hi everyone!
I’m new to openmc so there are some basic functionalities I don’t know how to use properly. I am trying to create a mesh filter to run a PWR simulation. My question is: how do I define the dimensions to create a mesh that gives me results of each fuel assembly of my core?
For example, I tried using from_rect_lattice (since I’ve defined my assembly w/ a rectangular lattice), but it didn’t work. As an alternative, I tried defining the dimensions, width, etc., but I am not sure if the mesh I’m creating is what I’m picturing.
I’m sorry if my doubts aren’t clear, but I’ve started using the code a couple of months ago as a grad student.