How is the VSEPR theory used?
VSEPR is short for Valence Shell Electron Pair Repulsion. It is a theory that basically says that electron pairs (bonding and nonbonding) of the central atom in a molecule will push as far away from each other as they possibly can in three dimensional space.
This means the bonding electron pairs in a molecule like
Here is a video which discusses other possible arrangements of electrons around the central atom and the shapes these arrangements will produce.
Hope this helps!