In the tester report which is generated when you run your test scripts, failed test cases are highlighted in red.
To debug a failed test case you should:
check that the input data is correct (open the test case to view and/or update the base level attribute values)
check that the expected results are correct (in the Test Report, click on the expected result to view and/or update the expected results for that attribute)
check whether outcomes are set correctly (in the Test Report, click on the outcome to view and/or update the outcome for the test script)
check the decision report (in the Test Report, click on the actual result to view the decision report for that attribute)