Force
A force is an interaction between two objects or systems, described by a vector and measured in newtons. It is never something an object owns on its own: name a force and you must be able to name both things involved.
AP Physics 1 states it as a learning objective rather than a formula. LO 2.2.A asks you to describe a force as an interaction between two objects or systems, and EK 2.2.A.1 says forces are vector quantities that describe the interactions between objects or systems.
Two objects, always. EK 2.2.A.1.i: a force exerted on an object or system is always due to the interaction of that object with another object or system. EK 2.2.A.1.ii closes the loophole: an object or system cannot exert a net force on itself. That single pair of statements deletes most invented arrows, because there is no other object supplying a force of motion, and none supplying an outward push on a car going round a bend.
Which is why forces come in pairs. Newton's third law is the same idea written as an equation, in EK 2.3.A.1. The two forces are the two sides of one interaction, so they act on different bodies and can never cancel on a single free-body diagram.
Units and symbol. The newton, N, equal to a kilogram meter per second squared. The AP equation sheet's symbol list gives = force.
Contact forces are not a separate species. EK 2.2.A.2 calls them the macroscopic effects of interatomic electric forces between an object and whatever it touches.
Adding forces up is the net force, and the routine for doing it is in how to find net force.