What happens to the particles in matter when hear energy is added to them

There are two possible situations.

1) If a phase change is not occurring, then the heat added contributes to increased translational energy of the particles. What that means is the particles move/vibrate faster.

2) If a phase change is occurring, then the heat added contributes to the breaking of bonds or intermolecular forces (depending on the chemical nature of the matter you're dealing with).