Enter data as Inputs and click "Simulate now". The rules that applied will be highlighted in the DMN table, and the Output data will be displayed. If there was a problem, you will see the DMN engine's error message.
Edit the FEEL Expressions in the Decision Table Cells. For example, [5..8] means "if the input is 5, 6, 7 or 8".
You can also change the Decision Table's Hit Policy.
Click on the little + in the table footer to add a table row (i.e., a new rule), or right-click on an existing rule to remove it. Rearrange the order of the rules via drag and drop by clicking on the number at the row's left end.
Click on the little + next to "Input" or "Output" in the table header. You should then specify a label and the data type . You will see the respective input or output as a new field above the DMN table, too.
Please make sure you are using Chrome or Firefox latest. Currently this Simulator does not work correctly with Internet Explorer.