At first, you should understand what is STP, as the above person said, STP stands for three words: Segamenting, Targeting and Positioning. So we need to explain these words one by one:
1.Segamenting: Because there are more than 17 million people in Shanghai, you need to divide these people to differen groups based on the income, gender, age,etc.
2. Targeting: After you define the different groups, you need know which group is your targeting market. You can use the Michael Porter's competition model and SWOT to analyse which market is your targeting market.
3. When you finish the above two steps, you need to position your product based on the features, benifits,customer's needs, etc. And you can do the marketing plan( Product, price, place, promotion) based on the three points.