How does molecular geometry affect bond angles?

The geometry of molecules depends on the number of atoms present in the molecule and the angles between bonds in the molecule.

For example, molecules $C {O}_{2}$ and ${H}_{2} O$ both have three atoms. The angle between bonds is 180° in carbon dioxide making this molecule linear. The angle between bonds in water is 104.5° making water a bent molecule.

The shapes of molecules have important implications. One is that even though both C=O bonds and O-H bonds have dipoles, carbon dioxide molecules are non-polar due to their linear shape and water molecules are polar due to their bent shape.

Here is a video which discusses VSEPR theory and molecular geometry.

Video from: Noel Pauller

Hope this helps!