Maven goals are accesible from the context menu of the project's main node.
It contains
predefined items like Build, Clean, Create Javadoc etc. These items are also accessible from
the main menu of the application or using keyboard shortcuts. (Eg. to build the project, press F11)
See the Project properties page to find out how to redefine what goals these actions run.
The "Execute Custom Goal" item let's you access the project's custom goals defined in maven.xml file
plus you can add the most commonly used items there. The last item in the popup ("More Goals") shows a dialog where you can
select any goals.

In the custom goals dialog, one can either enter the goals by hand
or select them in the tree of available goals. You can also enter any properties required.

While Maven is running, the output is printed to the console. Regular output is printed in black, errors in red. For compilation errors and for test failures, the important lines are marked as hyperlinks (in blue).
Clicking on compilation error link, shows the affected line in editor.
Clicking on test failure opens the Test source and prints the test results to the output console tab.