Draw a Spline
With the free-form spline tool you can draw a spline with your mouse directly within the viewport. Activate the tool in the left toolbar.
The spline color indicates its direction, from blue to white
Use your left mouse button to add a new point to the spline. Hovering over an existing point moves the point. A Right-click on the spline allows you to insert and delete points.
The spline color indicates the beginning and end of the spline. It starts from blue and changes to white.
To edit an existing spline, select it and run the free-form spline tool.