How do you set up a voicemail for your phone?

I have a nokia flip phone and my dad had it before me he had one set up and i tried to change it but now it goes to like a robot person and it says something about Gci how do i change that?How do you set up a voicemail for your phone?If you call your own phone number you can access your inbox, which is usually how you check your voicemail. If your voicemail isn't set up yet it will usually start walking you through it.