Set up multiple nodes and parameters at once.

ros2 pkg create hexa_robot_bringup 
# {robot name}_bringup : typical launch file naming rule.

cd hexa_robot_bringup
rm -rf include
rm -rf src
mkdir launch
cd launch
touch number_app.launch.py
chomod +x number_app.launch.py ## so we don't have to build everytime with symlink.

ros2 launch {hexa_robot_bringup} {number_app.launch.py}

Here is the format

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    ld = LaunchDescription()

    turtlesim_node = Node(
        package = "turtlesim",
        executable = "turtlesim_node",
    )

    turtle_spawner_node = Node(
        package="tuetlesim_catch_them_all",
        executable="turtle_spawner",
        parameters=[
            {"spawn_frequency": 0.5},
            {"turtle_name_prefix": "hexa_burbach"},
            ]
    )
    
    turtle_controller_node = Node(
        package = "tuetlesim_catch_them_all",
        executable="turtle_controller",
        parameters=[
            {"catch_closest_turtle_first": True}
        ]
    )

    ld.add_action(turtlesim_node)
    ld.add_action(turtle_spawner_node)
    ld.add_action(turtle_controller_node)
    return ld

in package.xml, add what you need extra.

<exec_depend>my_py_pkg</exec_depend>
<exec_depend>my_cpp_pkg</exec_depend>
**<exec_depend>turtlesim</exec_depend>
<exec_depend>tuetlesim_catch_them_all</exec_depend>**