After deducing the basic shape, we can deduce the real geometry base VSEPR theory.
Please try this simulation. You can add and remove the electron pair and observe the changes in molecular geometry.
Basic Molecular Shape also known as Electron Group Arrangement. To deduce the basic shape, we must draw the most plausible Lewis structure, and then, count the total number of electron pairs around the central atom.
Replusion VSEPR