A force can most easily be described as a push or a pull. When a force is applied to an object, the velocity of that object changes. This change in velocity constitutes an acceleration. So, forces are tied to accelerations. Galileo and Newton were scientists who developed our understanding of forces.
Galileo and the Concept of Inertia
Forces in General
Isaac Newton's Three Laws of Motion
Components of a force vector
The inclined plane
An understanding of forces should include an understanding of vectors.