Recording sessions allow you to record melodies you play on your MIDI keyboard in real-time. To start a recording session, turn on the Record button in the Transport panel. Now press the Play button (located in the Transport panel too). FruityLoops will play the song as usual, but will also record the MIDI events coming from your MIDI keyboard. You can select whether you want the melody recorded in the Piano Roll score of the channel or the Step Sequencer (see the MIDI settings page).
However, this is not all you can record during recording session. Except notes, patterns in FruityLoops can hold the value changes in time of any control that can be automated (for example, turning up the volume wheel of a channel, tweaking the cutoff of TS404 etc.). During recording sessions, FruityLoops records all changes you make in those automatable parameters (wheels, sliders, LCD-s, switches).
If you want to use one global events track for recording automation events (FruityLoops 2.x style), you can create a special pattern to hold automation events only. Then put a dot for it in the first bar of the Playlist, select it (so it shows in the Step Sequencer) and make your recording session. FruityLoops 2.x projects are imported using this solution - special pattern called "Main Automation" is automatically created and all events are placed in it.
You can cancel a recording session (so it does not apply the recorded notes and automation events) in two ways. The first one is to choose Cancel Current Recording command from Help menu, but note that you should do this while recording, BEFORE pressing the Stop button. If you press it, you can still undo the whole recording session by choosing Undo from the Edit Menu.