Valence Bond theory is a localized theory of chemical bonding. Again VB theory is a quantum mechanical theory that is now mostly used as a qualitative description of chemical bonding (in particular in organic molecules). It describes the bonds in molecules as arising from the overlap of atomic orbital centered on the atoms in the molecule. However, to achieve the correct geometries it must often use new "hybrid" orbitals that result from the mixing of some number of pure atomic orbitals. These new "hyrbridized" orbitals are degenerate (have the same energy) that is intermediate to the pure atomic orbitals. These new hybridized atomic orbitals occupy the correct regions in space that allow for the given electronic geometry around the atom such that head-on overlap can occur between individual atoms to give sigma bonds.
We use VB theory to describe the orbitals that give rise to the sigma and pi bonds in a molecule. Even though we often use VB merely as a qualitative theory it provides new insights into chemical bonding beyond what can be achieved from simple picture such as Lewis dot structures or VSEPR. For example, the VB model gives a better picture in particular of how to understand double bonds in a molecule as well as how to describe molecules that exhibit resonance.