Simulate
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.
Change Rules
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.
Add Rules
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.
Add Inputs/Outputs
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.