Through the "app settings" you can choose the artefact type that the chart is working on: Tasks, Defects, User Stories or Portfolio Items.
If you choose portfolio, then the 'type' field in the app settings is used as well.
In the main page of the app, you can select the field to do the plot against. This field is filtered to be one of the "drop-down' variety where there is a fixed list of 'states'
You can also select the dates to look for changes within. The filters are for changes that occur _between' the start date and the end date. The filters are not very accurate, so they try to work on a 'per day' basis. For example, if you create a story and it goes into the backlog state and you move it within the same hour to another state (e.g. Defined), the app will ignore it. If you take two hours to do it, then it will register as taking zero days.