Draw on a frame, write a note, point with the laser, check motion with onion skinning, and find every remark again in the notes tab.
You draw straight onto a frame to mark up a correction. The drawing belongs to that frame of the clip and stays there; the written note belongs to the clip. Both come together in the Review Notes tab.
Press P to show the paint tools, then pick one:
| Keys | Tool | Use |
|---|---|---|
Shift+Q | Select | Take a stroke, shape, arrow or text, move it or delete it |
Shift+W | Brush | Freehand line |
Shift+E | Eraser | Remove specific strokes |
Shift+R | Arrow | Point at an area |
Shift+T | Shape | Rectangle or circle around an area |
Shift+Y | Text | Click on the picture and type |
Shift+U | Laser | A red dot with a fading trail, leaving no mark |
Escape leaves the tool. Strokes are stored in picture coordinates: they stay in the same place at any zoom, any decode resolution and any window size.

Image: Sintel, (CC) Blender Foundation | studio.blender.org
In Complete the bar floats over the bottom of the viewer; in Essential it is the bar at the top of the viewer, the same tools in one row. On the capture:
Ctrl+Z), Redo (Ctrl+Y) and the bin, Clear all drawings on this frame (Ctrl+Shift+X), which Undo brings back.The dots at the left of the bar are a grip to move it; a double-click puts it back in its place.
Shift while drawing: with the brush, a straight line from the last point; with the rectangle, a square; with the arrow, an angle in steps of 45°. The circle is always round.Delete erases it, Escape lets it go.Ctrl+C copies the selected stroke, or every drawing of the frame when nothing is selected; Ctrl+V pastes them onto the frame on screen, in the same place.Onion skinning ghosts the strokes of the neighboring frames under the current one (the strokes only, not the picture). It is how you check that a note follows the motion instead of jumping about. A click turns it on; its arrow, or a right-click, opens its settings: how many frames before and after (0 to 10, 2 by default), the opacity of the nearest one (50% by default, the farther ones fade) and Keep original colors. Unticked (the default), the frames before are tinted red and the frames after green.

You draw on the picture you see. In A alone the stroke goes on A, in B alone on B. In the wipe it goes on the side where it starts, even if it crosses the divider. Each drawing belongs to the clip and the version of its track; in Review Notes it is labeled A v003 or B v004.

The Review Notes tab of the Media & Session panel gives every clip its own note box:
Ctrl+Right and Ctrl+Left jump to the next or previous annotated frame: a way to walk through every remark without hunting for it.Each note is a card: at its head, the clip's name and version, its frame count and number of drawings, and its status pill (Approved, Not Approved or Pending), which opens the status menu. Each drawing is labeled with its track and version (A v002) and its frame number and timecode. At the top of the tab, Only annotated shots hides the clips without a remark.
Notes and drawings are saved in the playlist (.bpl). To take them out of the player, see Notes and export; to send them to a tracker, see Trackers.
Going further: the complete manual, part 5 (Help > User Guide).