Logbooks are required to be kept updated, along with an electronic on board recorder.
A logbook simply records all trips, and times, up to the 15-minute hour divisions. Every logbook is required to have multiple copies. These copies generally are carbon copies, so that each can be held at the home office, and with the driver (the driver keeps the book).
The electronic recorder is more of an electronic version of the logbook. It records the same types of information (time, location). The driver really only must focus on putting his hours/rest periods in the machine.