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.

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.