Hi, if you have little difficulty, you can learn at the Apple Support here https://support.apple.com/en-us/HT201436
The telephone systems have the feature named as Voicemail. VoIP is the best example of it. When a receiver is unable to pick up the phone, then the caller can leave the voice message on the receiver’s phone. In older telephonic machines, such messages were stored as a voice message directly, and the receiver can hear them later. In modern telephone systems, such info is being stored on the server of the service provider in the user’s mailbox. It is similar to email in which the messages are saved in the form of audio instead of text.

The Android operating system includes a native visual voicemail that lets you view voicemail messages in text form. If you have an older Android phone or if your service provider doesn’t offer visual voicemail, you can download a third-party app. Select Phone. Select Keypad. Press and hold the number 1. If your voicemail is not set up, select ADD NUMBER. Select Voicemail number. Enter the Voicemail number and select OK. Repeat steps 2-4 to check your voicemail.
Step 5. Tap “Stop” to end the recording. Then, tap “Save.” You can open your recordings in the top-right corner of the screen.