First, drag the marked molecule to the cluster. The molecule collides the cluster and scatter the molecules of the cluster. After the collision, the speed of molecules get faster and move freely. The state is called "Gas". If any molecule collides to the wall, the speed of it changes slower because of the wall absorb the energy. After many collision to the wall, the speed of molecules gets slower and make cluster again because of Intermolecule force. And the state changes to "Liquid' and "Solid" as the speed gets slower.