Fronts are lines that help you align your fireworks.
They exist only for convenience. You can place fireworks anywhere, not just on fronts!
Select the “Fronts” tab in the sidebar:
Click the buttons in the sidebar to add or remove fronts. Move the fronts by dragging the circles in the 3D view.
If you move a firework near a front, it automatically snaps to it. The front becomes blue if the firework is snapped to it.
To disable snapping, hold the CTRL key.
If a firework is snapped to a front, and you move the front, the firework moves too.
The start and end points of steppers can be on different fronts: