A collection of particles is created in a random position with random velocity - each particle has a particular desired target position on the edge of one of the words above.
Each particle wants to be at its desired position and so moves according to a desired force which would take it straight to its desired location if it was standing still. Unfortunately... each particle already has a random starting velocity and so a steering force is calculated in order to correct the path of the particles.
Additionally the particles are acted upon by a repulsive force from the mouse position to further complicate matters.
Using the options above you can experiment with interesting combinations of simulation variables.