Marking events is a way of visually selecting time points and saving them in the
stageData.events struct. You can use this feature to visually identifying rapid eye movements in order to calculate REM density or to mark arousal events. If you have events from bio-calibrations you can also import those using a notes file and see the events in the record.
To start marking events, either use the "Mark Events" menu or the cross icon on the toolbar to turn on event marking mode. This will turn your cursor into a cross hair so that you can start selecting data points. Note that when you are in mark events mode, you will not be able to use the keyboard shortcuts, you can use the buttons instead. Here is a display of all the event marking features: