What you are describing is a web application. It's debatable whether you need to implement an Android app for this at all. An app would really be a simple webview wrapper, so why not use the web browser instead?
Your system will involve a central server component, with a database. Customers will use their mobile devices to communicate with the server, and submit orders. This is a classic web application, accessed with the web browser on the user's device.
So all the work will be done on the server - you need to create web pages, possibly javascript, and also some server side code (PHP is probably the easiest way to implement it). Plus a database.
Implementing this as a web application also means that your users can access the service on a desktop computer, not just mobile devices.