I'm trying to learn and understand the ECS (Entity Component System) so that I can create a game using this design pattern but I've got a lot of things that I still don't understand.
Lets say I've got a PositionComponent and a MovementSystem or PhysicsSystem. The PhysicsSystem will heavily rely on the PositionComponent since in order to calculate, for example a rigid body motion, it needs the x and y positions (in a 2D game) wich is contained by the PositionComponent.
What is the relationship between Components and Systems? How does the MovementSystem get the x and y values from the PositionComponent?