How do you change i phone to vodafone?

I just bought a second hand i phone and have no idea how to unlock it or to fit my vodafone sim card. Im not sure if I have all the instructions as there is no mention of how to add your number. Am I missing something really basic?How do you change i phone to vodafone?i think it will work on Vodaphone, just go to the nearest vodaphone company and ask for help, or unlock you iphone, you can search for the unlock on youtube , there is millions of videos that tech you to do it.

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