Redirect caller to voice mail

Hello everyone,
I like to redirect my callers after conversation in to the voice mail.
when the operator hangup the call redirect caller in to the voice mail, my voice mail number is 9001.

I thinks should be insert any code in to the extention_additional.conf…!!!

please advise me to do that.

Thanks in advance.

extensions_additional.conf is not referenced by or included in the standard distribution of Asterisk. You are probably using FreePBX, which is supported at freepbx.org/forums/