system. system has input/output ports that could be connected with other systems. A system block can be a diagram or a leafsystem. leafsystem is the minimum build block and a diagram is composed of multiple leafsystem or diagram.leafsystem functions as basic components in robotics systems, like signals, sensors, controllers, planners, etc.diagram to represent systems that internally have several connected systems that function as a whole. diagram itself is a system and can be nested. The root diagram contains all the sub-systems and sub-diagrams.diagram.context is data of system states and parameters cached in a separate place. Each diagram and each system has its own context. The context and the diagram are the only two information a simulator needs to simulate. Given the context, all methods called on a system should be completely deterministic and repeatable (ref. Underactuated Robotics textbook).diagram->CreateDefaultContext() which creates the context with default values for all the subsystems. Values in the context, such as the initial state and the initial time, can be independently set before the simulation begins.simulator takes in the system diagram together with its context, to simulate by updating parameters such as integral continuous state derivatives, compute discrete state updates, allocates the various outputs of a system, etc.diagram that contains a unique leafsystem namedMultibodyPlant is considered as a robotic system. MultibodyPlant internally uses rigid body tree algorithms to compute the robot kinematics, dynamics, jacobian, etc. MultibodyPlant is a system. So it has input/output ports that could be connected to other systems like controllers and visualizers.MultibodyPlant for simulation.