I have'nt under stood below topics in the video and need a deep explaination

3) difference between mkdir India/Mumbai and mkdir -p India/Mumbai

The pushd command is used to save the current directory into a stack and move to a new directory. Furthermore, popd can be used to return back to the previous directory that is on top of the stack.

It is very useful when we have to switch between two directories frequently.

mkdir India/Mumbai >>> will create directory Mumbai if directory India already exists, else will show error. While mkdir -p India/Mumbai will create both directories at once.