Visit your home in World Tour and from the home screen highlight 'partner list'. You shouldn't have anybody in this list if you are ranked around 70 or above in the Amateur Tour. To unlock this, you need 8 people to occupy the list. As I said, when you start making good progress in the rankings you will be invited to a practice match with a fictional character. Read the date he has set and when this date rolls around go to the location on the map corresponding to the match. I'm not sure if you have to win the match to befriend the opponent but you will probably win anyway. Repeat this process 7 times with different characters.