Systems contain the logic that processes and manipulates entities based on their components. A system will typically operate on all entities that have a specific set of components. For example, a “Movement” system might update the position of a “Position” component Create a movement system with with 
bolt system system-movement
which will add a new component to your workspace: 
use bolt_lang::*;
use component_position::Position;

declare_id!("FSa6qoJXFBR3a7ThQkTAMrC15p6NkchPEjBdd4n6dXxA");

#[system]
#[program]
pub mod system_movement {

    pub fn execute(ctx: Context<Components>, args_p: Vec<u8>) -> Result<Components> {
        let position = &mut ctx.accounts.position;
        position.x += 1;
        position.y += 1;
        Ok(ctx.accounts)
    }

    // Define the input components
    #[system_input]
    pub struct Components {
        pub position: Position,
    }
}
In this simple example we have created an entity Player that holds a Position component with x,y,z coordinates. We can execute the movement system to change its state. For a more sophisticated movement dynamic, let’s define a Velocity component: 
use bolt_lang::*;

declare_id!("CbHEFbSQdRN4Wnoby9r16umnJ1zWbULBHg4yqzGQonU1");

#[component]
#[derive(Copy)]
pub struct Velocity {
    pub x: i64
}
Someone might want to introduce a new power-up for faster movement. They could do this simply by adding a new system that acts on the Position component using Velocity 
#[system]
pub mod system_apply_velocity {

    pub fn execute(ctx: Context<Components>, _args: Vec<u8>) -> Result<Components> {
        ctx.accounts.position.x += ctx.accounts.velocity.x;
        Ok(ctx.accounts)
    }

    #[system_input]
    pub struct Components {
        pub position: Position,
        pub velocity: Velocity,
    }
}
This new system takes as inputs the Position and Velocity components, and defines the logic of the power-up. There is no notion of Solana accounts or CPI - the proxy World program is taking care of everything.