How to provide web application for browser, android and iOS

I am making a web application. I want that it should cater for browser based apps (including browsers in mobile phones.. which I understand stuff like bootstrap can cater for). But I also want it to cater for Android and iOS apps. How can that be done? I am particularly interested in project structure, build and release. What are the files and how will they be laid out. How will my app figure out what kind of client has made a request, and how does it direct the request to the right set of files. Thanks.