May 15, 2019 · The three dashes (“—“) merely separate the lines of file 1 and file 2. As a summary to make both the files identical, first add Tamil Nadu in the first file at very beginning to match line 1 of second file after that change line 2 and 3 of first file i.e. Uttar Pradesh and Kolkata with line 3 of second file i.e. Andhra Pradesh.
find is the Unix command line tool for finding files (and more). -ls lists the resulting files (the files that have been modified in the last N days) in ls -dils format on standard output. You can skip this, but using it you'll get more information like the file size, permissions, the modification date, etc.