There is a default greeting when an inbound call goes to voicemail - but a custom voicemail greeting makes for the best customer experience.

1.  To see your Voicemail and set a Greeting, click on the Bell Icon next to your username in the top right corner of any page.  

2.  Next to the Voicemail tabs - click the drop-down menu, and choose Edit Voicemail Greetings

3. Click the option to Edit Greeting, and you will be able to record your own custom Greeting.

Alternate option

System Voicemail Greeting

Note: Your Admin may have set the option for you to use a System Greeting as a default. You may need to check with them before changing the default.