Well...the 'formal' way would be 'My name is Jo Okazaki' and this could be used in a reply to questions such as, 'What is your name?' or 'Could you tell me your name?'
'I am Jo Okazaki.' is also usable in the same situations as above but also could be used in situations where let's say, you are at a party and someone comes and asks you, 'I am looking for Jo Okazaki. Do you know them?' You could respond with, 'I am Jo Okazaki. Can I help you?' But again you can just as easily use, 'My name is Jo Okazaki. Can I help you?'
They are both interchangeable.