Bundle is something similar to class in OOP for our Entity. It helps you create easily an entity with set of Components.

Bundle as a struct

To create a bundle, pass the trait Bundle before your struct:

#[derive(Bundle)]
struct PlayerBundle {
	health: f32,
	sprite: SpriteSheetBundle,
	marker: Player,
}

Then, you can spawn the bundle in setup system:

fn setup(
	mut commands: Commands
) {
	commands.spawn(PlayerBundle {
		health: ...,
		sprite: ...,
		marker: Player,
	});
}

If you want to create an entity with default value, u can derive the Default trait for it:

impl Default for PlayerBundle {
	fn default() -> Self {
		Self {
			health: ...,
			sprite: ...,
			marker: Player,
		}
	}
}

You can then spawn Player like this:

commands.spawn(PlayerBundle {
	health: ...,
	..Default::default()
})

Common mistake

U might think that you can query components by using bundle. But that is wrong. You should always do Query<(&Component1, &Component2, ...), With<Marker>) instead.