I have never used any UML software before, and I may be missing (more than likely am missing) some steps to get my diagrams to show accurate information.
I am using Windows 10, Android Studio 2.3.3, PlantUML plugin, and the graphviz plugin. I think that's all the pertinent system info needed, but if I missed anything, just let me know and I'll fill in the missing details.
I need to reverse engineer our code into Class, Sequence, and possibly UseCase diagrams. Here are the steps I've taken to get my current diagrams; which none of them have any details in them.

I r-click on the folder or I want to have diagramed >> New >> UML Class
No matter how deep I dive into the source code and regardless if I select a folder or individual file, the output is always the same. This happens for all the UML diagrams, which leads me to believe I'm missing something.
I have looked for documentation to reverse engineer Java code to PlantUML diagrams, but I have not found anything that makes sense to me. Any help you can offer is appreciated, thank you.