What is the Piano Roll?

Use Ctrl+4 to open the Piano Roll.  You will see a vertical piano keyboard along the left side of the window.  Notes from selected tracks are represented as solid rectangles to the right of their corresponding notes on the keyboard:

Can I add and edit notes in the Piano Roll?

Before drawing notes, you should select a single track to work with.  Select the note duration using the same toolbar icons as described for the Staff View.  Select the pencil tool, then click in the Piano Roll view.  You may move the cursor in any direction until the correct note and position are achieved before releasing the mouse button.  When you click on the view, and as you move the cursor, the note will be played on your synthesizer.

To move a note, click it, drag it to a new position, then release the mouse button.  To copy a note, hold the Shift key as you do this.

Multiple notes may be selected by drawing a selection rectangle.  Select the Arrow toolbar icon, then click in the window (note one a note) and move the cursor.  Notes that overlap the rectangle will be selected.   Additional notes may be added to the selection by holding the Shift key as you click on them or draw more selection rectangles.  Note selection may be "toggled" by using the Ctrl key instead of the Shift key.  Your selection of multiple notes then may be moved (by clicking on any note and dragging) or copied (by holding the Shift key while clicking and dragging).

Position the cursor over the right-hand edge of a note to move its ending point (duration).  When the cursor becomes a double-headed arrow, click and drag the edge to a new position.

Right-click on a note to edit its properties.

Are drum tracks handled any differently?

A drum track is one that is using a patch that you've identified as a drum patch in the synthesizer database, or is using a channel that you've identified as a dedicated drum channel.  When you select a drum track, note names are displayed to the right of the keys on the piano keyboard:

Can I "play" the piano keyboard?

Yes, you may audition notes by clicking on the keyboard.

First, I play in a rock band and was looking for a nice Midi
sequencer that can be use to play live jam/gig and also have FULL
control over the midi. Having a Start button, with TAP for tempo, and
also playing the introduction until I decide to start the song was a
most. Other sequencer I found did'nt give you the control like
MidiMaestro does.--Steve Hollingsworth