The Force field is the simplest of the fields. It gives a constant force towards (positive strength) or away from (negative strength) the object’s center. Newtonian particles are attracted to a field with negative strength, and are blown away from a field with positive strength.
For Boids Particles a field with positive strength can be used as a Goal, a field with negative strength can be used as Predator. Whether Boids seek or fly goals/predators depends on the Physics settings of the Boids.