London forces also known as "induced-dipole-induced-dipole interactions" and are in principle found in every molecule. The interaction occurs from the transient dipoles all molecules have as a result of fluctuations in the instantaneous positions of electrons.
Dipole-dipole arises when we are able to set up a polarity in the molecule. So for an example if a highly electro-negative atom is bond to a less electro-negative atom then there will be a polarity in the molecule and we therefore have the dipole-dipole interaction.
For the determination of geometry for the specific examples , use the VSEPR (Valence Shell Electron Pair Repulsion) model and by that determine the geometry.
