1. Add an expense or category from the left panel.
2. Drag an expense over a category to add it to that category. An expense can belong to multiple categories.
3. Click on any expense or category to view it in detail. While in detail view, take actions (delete, edit, close).
About
This simple expense-tracking app is an accompaniment to a blog post on D3+React+Flux. The blog post itself is being slowly written, but in the meanwhile, you can find the source code here.
A caveat: there's no backend implemented, so all of the data is stored locally on the client. This means that the data will not persist across browsers.