Quick tutorial

Download px4 + gazebo then in px4 folder

make px4_sitl_default gazebo

Download QGroundControl and:

chmod +x QGroundControl.AppImage

Download ROS Melodic desktop only version

Download mavsdk newest version

Make catkin_ws folder, add this repo to src and catkin_ws folder:

catkin_make

if everything is okay

roscore
rosrun mavsdk_interface node udp://:14540
source devel/setup.bash