Hello, I just would like to know the different types of formulas for moles... Example: Molecular, empirical, etc. I would like to know them for an upcoming test. Just to refresh my memory

I don't understand--molecular and empirical formula?

When you have grams of a substance, then mols = grams/molar mass = ?
If it is an element and you have grams then mols = grams/atomic mass = ?
For solutions, mols = M x L = ?