This is shell script, Shell has many version and first line of code "#!/bin/ is to  tell to which type of shell is used to execute that script.
The most  famous shell are korn shell (ksh) and bash shell (shell). Although unix scripts can execute in all shells but some commands (very small list) are very specific to that shell type so we need to give shell type in accordance.

Otherwise "#" is used to comment in unix (if it is not first line in script and it is first character of that line).