What's the key difference between Heterogenous refinement and 3D classification?

[CryoEM2]

Analysing flexibility and heterogeneity in cryosparc

Dear community, since there are quite a few tool in cryosparc that aim at tackling/resolving heterogeneity and flexibility of macromolecular complexes I would be grateful if someone could briefly summarise major differences between them, when typically they should be used and how to make the most out of them. I refer to the following jobs: 3D Variability 3D Classification Heterogenous Refinement Local Refinement anything else? many thanks, p