...
There are many clickable items in the dashboard, the most useful is usually to click the number under the "Test" column of the tests you want to see (usually failing tests are the most interesting to probe, so you'd click the number in the "Fail" sub-column). This will take you to a page with some data about the test run at the top and a list of tests that had a specific result. The most useful data at the top of the page is presented in the Out-of-the-Box (OOTB) field named "OS Version." Jim Foucar configured this field to display the sha1 of the commit that was tested (it is not possible to rename the field though). Below the general information is a list of tests, and again, there are many clickable items. The most useful clickable item for a test is it's Status field. Clicking this will take you to the TestStatus.out data for the test, which should help to give you some clue as to what happened.
Getting Log Data for Failed Tests
In many cases the TestStatus.log file will not have adequate information to diagnose a problem. For build and run failures, log files for the problematic test will be automatically uploaded. If results are available you'll see a gold cube next to the top-level results for a machine/compiler/branch on the main page:
The gold square highlighted in red indicates that log files are available to download for the acme_test_only_next_gnu build. Unzipping and untarring this file will yield a directory tree in which there is a subdirectory for each failing test that will have the relevant log files.