Comments are used to document the source code. Comments make the Program more readable.
Suppose you written thousand lines of program, without proper documentation, after some time, for the owner of the application also, it is very difficult to figure out what was written.
By using comments, you can document your code at the time of writing program. Comments won't affect your program execution. Comments simply document your code.
How to write comments in batch script?
Using Rem Command, you can record the comments in a batch file.
Any text followed by REM command is treated as command.
Microsoft Windows [Version 10.0.16299.547]
Volume in drive C is OSDisk
Volume Serial Number is 1034-4F6F