A force is an interaction which, when unopposed, causes the change in the state of motion of the object. That is it changes the velocity of any object having mass.
Force can be measured the rate of change of momentum. Also acceleration times mass is the froce. (F=ma)
There are total four types of force, 1) gravitational force, 2) electromagnetic force, 3) strong nuclear force and 5) weak nuclear force.
The SI unit of force is Newton (N) and dimension of force is [MLT-2].