Post-simulation analysis

GROMACS version: 2021.4
GROMACS modification: Yes/No
Here post your question : After simulating my protein in different solvents and at interface of hydrophobic-hydrophilic surface, for RMSD analysis, what groups should I select from choices (in the tutorial it’s given to choose “Backbone” for both the least-squares fit and the group for RMSD calculation)? How does this work? Can you explain me how to decide the choices? Is it the same for RMSF analysis?