This is a big topic. You'll definitely want to be able to walk before you can run. Here are some resources to get you started:
At a minimum, you will need to have a working understanding of HTML, CSS, and JavaScript for the front-end of the website, a server language and platform such as PHP, C#, or node.js (or others) for the server back-end, a database system such as MySQL or SQL Server for the database layer, and Java for the Android app. If you aren't at an intermediate level at all of those (or know someone who is), it could very well take you more than a year to learn everything you need.
Also, your requirements are strangely difficult: it's not common to see a "wifi-only" website that runs a database and communicates with an in-range mobile app. It may be technically possible, but it would be extremely difficult to do. The most common architecture is one where both the website and the mobile app would communicate with the same remote server (which handles the database connection). No server and local-only communication would require some significant and unusual engineering.