Android App to online shopping:-
First, when app run - get the user location, then show the super markets.
Second, When user choose the super market (Ex: market X), go to new page to show the all the items that related with market X.
Third, the customer can add all the items that he want, and go to payment and checkout.
When the customer reach the payment page, the App ask him about his Mobile number and sent activation code to him.
after that, the order hold in the Orders Lists to pick up it by the delivery boy.
that's quick abstract, the details later.