F adds a new point to the ROI selected in the ROI Manager list. If no ROI is selected, it creates a new ROI with one point. If you want to make a new ROI, first use deselect shortcut (see below).
G removes/deletes the last point added to ROI.
H deselects ROI (or stops tracing).
E selects the ROI closest to the clicked point.
Y reverses the order of points (first becomes last and vice versa). Flips ends for curve ROIs.
T in semi-auto trace mode moves TraceBox, so it is positioned around the last added point.
R in semi-auto trace mode connects two points with a straight line, rather than a trace.
V in semi-auto trace mode starts a new trace at the clicked location.