The Customer Relationships are the contacts with the customers that allow us to make an appropriate transfer of our Value Proposition. Customer Relationships are of three main types: customer acquisition, customer retention and boosting sales (upselling).
In other words you need to attract the customers into buying your product, you need to keep them coming back again next time and you need, if possible, to buy even more next time, or maybe even tell others about the product in a positive way.