Quick solution I discovered as a new user:

1. Object Mode: Add->Curve->Circle
2. Tab (edit mode) & A until everything is unselected
3. Select handles on opposite sides (say on the Y/green axis) and X to delete them
   (must be deleted as a pair to keep symmetry)
4. Select the END of one of the 2 remaining handles (on the X/red axis) and rotate 180° R X 180 Enter
5. Optional: Select both handles with A, scale with: S Y 0.5 Enter

Quick solution I discovered as a new user:

1. Object Mode: Add->Curve->Circle
2. Tab (edit mode) & A until everything is unselected
3. Select handles on opposite sides (say on the Y/green axis) and X to delete them
   (must be deleted as a pair to keep symmetry)
4. Select the END of one of the 2 remaining handles (on the X/red axis) and rotate 180° R X 180 Enter
5. Optional: Select both handles with A, scale with: S Y 0.5 Enter

Turn it into a tube:

1. Shape: Resolution: Preview U: increase to smooth curvature
2. Shape: 3D
3. Fill: Full
4. Geometry: Bevel: Depth: increase as desired
5. Geometry: Bevel: Resolution: increase to desired smoothness of tube
6. Active Spline: Smooth should be checked

Quick solution I discovered as a new user:

• Object Mode: Add->Curve->Circle
• Tab (edit mode) & A until everything unselected
• Select handles on opposite sides (say on the Y/green axis) and X to delete them (must be deleted as a pair to keep symmetry)
• Select the END of one of the 2 remaining handles (on the X/red axis) and type: R X 180 Enter
• Optional: Select both handles with A, scale with: S Y 0.5 Enter

Quick solution I discovered as a new user:

1. Object Mode: Add->Curve->Circle
2. Tab (edit mode) & A until everything is unselected
3. Select handles on opposite sides (say on the Y/green axis) and X to delete them
   (must be deleted as a pair to keep symmetry)
4. Select the END of one of the 2 remaining handles (on the X/red axis) and rotate 180° R X 180 Enter
5. Optional: Select both handles with A, scale with: S Y 0.5 Enter