The procedure is: find a testing session and take the test (have your FRN handy, and tell them that you're going for your Extra). When you pass the test, you should immediately get a Certificate of Successful Completion of Examination. That entitles you to operate using Extra privileges with a "/AE" callsign suffix right away. Once the examiner submits the test results to the FCC and the FCC processes it (usually within a few days), they'll issue your new license, and you can drop the /AE suffix. As you said, there's no practical test anymore, just the written, so that's all there is to it.
As for study materials, I can also recommend HamStudy. It's a good and principled resource, and their practice tests are really a good way to gauge how ready you are, and which areas you need to study more.