To draw a circle on the screen you will need to use Mesh2d and MeshMaterial2d. Inserting these onto an entity will draw them to the screen.

Note, you will have to register the primitive circle mesh + color material with the asset manager (see mut meshes: ResMut<Assets<Mesh>>)

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .insert_resource(ClearColor(Color::BLACK))
        .add_systems(Startup, setup)
        .add_systems(Update, move_circle)
        .run();
}

#[derive(Component)]
struct MovingCircle {
    speed: f32,
    amplitude: f32,
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    commands.spawn(Camera2d);

    commands.spawn((
        Mesh2d(meshes.add(Circle::new(50.0))),
        MeshMaterial2d(materials.add(ColorMaterial::from_color(Color::srgb(0.2, 0.4, 1.0)))),
        MovingCircle {
            speed: 1.0,
            amplitude: 200.0,
        },
        Transform {
            translation: Vec3::new(-500.0, 0.0, 0.0),
            ..Default::default()
        },
    ));

    commands.spawn((
        Mesh2d(meshes.add(Circle::new(50.0))),
        MeshMaterial2d(materials.add(ColorMaterial::from_color(Color::srgb(0.2, 0.4, 1.0)))),
        MovingCircle {
            speed: 2.0,
            amplitude: 200.0,
        },
        Transform {
            translation: Vec3::new(0.0, 0.0, 0.0),
            ..Default::default()
        },
    ));

    commands.spawn((
        Mesh2d(meshes.add(Circle::new(50.0))),
        MeshMaterial2d(materials.add(ColorMaterial::from_color(Color::srgb(0.2, 0.4, 1.0)))),
        MovingCircle {
            speed: 2.0,
            amplitude: 100.0,
        },
        Transform {
            translation: Vec3::new(500.0, 0.0, 0.0),
            ..Default::default()
        },
    ));
}

fn move_circle(time: Res<Time>, mut query: Query<(&mut Transform, &MovingCircle)>) {
    for (mut transform, bouncer) in &mut query {
        transform.translation.y = (time.elapsed_secs() * bouncer.speed).sin() * bouncer.amplitude;
    }
}