Draw a straight line:
select drawing tool (pencil icon)
select line size
click (and release) start point
press and hold shift
move mouse to end point, click and release, release shift
Draw horizontal and Vertical lines:
as above, but hold down shift and ctrl
lines are restricted to 15deg increments (ie. 0deg, 15, 30, 45, 60, 75, 90deg, etc.)
Draw Circle:
select "Ellipse Select" tool (icon near top left in Toolbox)
or Tools (top menu bar) > Selection Tools > Ellipse Select
may need to enter 1:1 in aspect ratio field
position cursor, left-click&hold,
press & hold shift+alt,
drag cursor to size desired,
release left-click
Draw a Solid Dot:
Edit (top menu bar) > Fill with FG color
-OR- Draw a donut or ring:
Select (top menu bar) > Border
enter border width pixels, click OK
Edit (top menu bar) > Fill with FG color.
Select (top menu bar) > None to release selection
Draw a Rounded Rectangle:
Using Tools > Selection Tools > Rectangle Select,
CLick & Hold, drag and release to create rectangle
Select (top menu) > Rounded Rectangle
Change radius % if desired.
Click OK
Create border:
Select > Border
Enter desired parameters, click OK
Fill border:
Edit (top menu) > Fill with FG color (or whatever desired)