Hello @abdulbasitisdost,
I think you should have a look at the ROS Basics course before going for more advanced courses since it will provide you a basic understanding of these basic concepts, like how launch files work.
Summarizing:
- pkg contains the name of the package which contains the program (ROS node) you want to start.
- type contains the name of the program (executable node in this case) that you want to start.
So, here you are launching a ROS program (executable node) named map_server from a ROS package which is also named map_server.
The error you are showing in the image is telling you that the program is looking for a map file named my_map.yaml in the path /home/user/src/catkin_ws/ and that the file is not there. So probably you will need to correctly set the path where this map file is located.
Best,