I'm on an assignment to create a java program with certain specifications.

The first thing that I have to do, is to hand in a planning of my work, consisting of "class diagram with function descriptions and flowcharts for critical functions" (translated from Swedish). However, I've never created any such diagrams or descriptions before, and while my current drafts might be acceptable, I was wondering if anyone got any tips for creating such documents, if there are any especially good tutorials for this or if there are any programs that help doing this that can be recommended for a beginner.

If you got any knowledge or experience of any of this, please share