Answer
The basic idea is that electron pairs repel each other, whether in bonds or lone pairs, and that affects how the overall shape of a molecule or compound will be.
Work Step by Step
A central atom has two types of electrons in its valence shell, either electrons in lone pairs or electrons that participate in bonds, Based on how many electron pairs your central atom has, and the type of electron pairs present, the molecule tries to minimize its repulsion as much as possible. The repulsion between two lone pairs is the highest while the repulsion between two bond pairs is the lowest. Using all this, the VSEPR theory attempts to predict different properties of a molecule, quite effectively at that.
