ROS WIKI

cd src
ros2 pkg create --build-type ament_python your_package_name

ros2 pkg create --build-type ament_python --node-name navigate_to_target turtlebot_navigator
#This will create a new package called turtlebot3_navigator with a Python node named navigate_to_target.

#to include srv
ros2 pkg create --build-type ament_python --license Apache-2.0 service_bot --dependencies rclpy bot

source ~/ros_ws/install/setup.bash

cd ~/ros_ws
rm -rf build install log

cd ~/ros_ws
colcon clean --packages-select alphabet_publisher_pkg #clean any deleted pkg file
colcon build --packages-select alphabet_publisher_pkg #normal build

colcon build --packages-select action_py --symlink-install #if you use this, No need to build each and everytime. Just the source file .bashrc

ros2 topic echo /topic_name

cd ~/ros_ws
rm -rf build install log

colcon build --packages-skip-build-finished --symlink-install
colcon clean --packages-select lidar_bot

chmod +x service_server.py

ros2 pkg create my_robot
mkdir srv action msg

#CMakeLists.txt
find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "action/CountUntil.action"
)

ament_export_dependencies(rosidl_default_runtime)

#package.xml
<buildtool_depend>rosidl_default_generators</buildtool_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>

#!/usr/bin/env python3
import rclpy
from rclpy.node import Node

class MyCustomNode(Node):  # MODIFY NAME
    def __init__(self):
        super().__init__("node_name")  # MODIFY NAME

def main(args=None):
    rclpy.init(args=args)
    node = MyCustomNode()  # MODIFY NAME
    try:
        rclpy.spin(node)
    except KeyboardInterrupt:
        pass
    finally:
        node.destroy_node()
        rclpy.shutdown()

if __name__ == "__main__":
    main()

#1
ros2 launch alphabet_publisher_pkg start_publisher.launch.py
#2
ros2 launch alphabet_publisher_pkg conditional_launch.py
ros2 topic echo /topic_name
#3 
ros2 interface show robot_interface/msg/PositionFeedback
#4
ros2 launch turtlebot3_gazebo turtlebot3_house.launch.py
ros2 run turtlebot_navigator navigate_to_target
ros2 run turtlebot_navigator odom_subscriber 

#1
ros2 run action_py obstacle_avoidance_server
ros2 run action_py obstacle_avoidance_client 

#1
ros2 run my_package turn_server
ros2 run my_package turn_client "Turn Right"