Vibrato is the rhythmic, cyclic fluctuation of volume that spontaneously happens (or is created) when keeping notes for a long time. Adding some vibrato to such notes will add a very realistic feel to your melody. Click on the VIB icon on the toolbar to toggle its display. It appears as a light green line/curve over the cells, as shown here:
By default, no vibrato is defined (so the green line appears fully horizontal, at the bottom). You can define vibrato curves across your sequence by selecting the Components > Set LFO Envelope option. You will then see the following LFO panel:
Here you can tailor your vibrato curve by adding, removing or moving points. A click on an empty area of the graph will add a point. A click on a point, or dragging a rectangle around one or more points will select them. You can then drag them to another position or press the delete key to delete them.
To save your changes, click on APPLY.
To remove any vibrato, click on CLEAR.
To leave without saving the changes, click on CANCEL