New to Java

Hi,

I'm new to Java and I want to try a little project to boost my knowledge a little bit.
I thought to get started I should write a small UML scheme to visualize it a little bit better, but since my UML knowledge is also poor I came here for some help. My programming is mostly in C# & PHP (HTML, CSS, XML etc).

I'm going to build a small application to support an existing back-end system. The back-end system is a recommendation engine.

The front-end should be an application which does the interfacing with the back-end system. Via this application the end user should be able to give his preferences, get his recommendations and give feedback.

I have no idea how to start, but I'm currently looking into UML and how to make a scheme for this.