Use the B-Spline tool
The B-Spline tool lets you build B-spline paths by positioning a series of anchor points that indicate the direction the path should follow. Each anchor point on a B-spline path can be a curve or corner control point.
To create a B-spline path
In the Toolbox, select the B-Spline tool.
Click anywhere in the document to set the starting point of the path.
Drag the pointer, watching the line to see how the curve segment will look. To constrain the position of the anchor point relative to the previous point, hold down the SHIFT key when you drag.
Click to position another anchor point. To create a sharp corner, hold down the ALT key when you click.
To end the path, do one of the following:
To create a closed path, position the pointer on top of the first node (the starting point) and click.
Double-click at any point to position an ending node.
Press ENTER or ESC to end the path at the last-positioned node.
You can remove the last node you added by pressing the BACKSPACE key.
The angle of the rotation depends on the value set in the Options dialog box.
To set the number of rotation steps
On the Edit menu, point to Options, and then click Units and Grids.
In the Units and Grids panel, under Arrangement, adjust the number of Rotation steps.
To append a B-spline path to an existing path, you must first enable the Drawing tools append to path option.
To enable the Drawing tools append to path option
On the Edit menu, point to Options, and then click Stroke.
In the Stroke panel, under Stroke, select the Drawing tools append to path check box.
With this option enabled, you can easily extend an already-existing path.
To add to an existing path
In the Toolbox, select the B-spline tool.
Do either of the following:
Place the pointer over the starting or ending point of an existing path and draw.
Create a new path and end by clicking the open point of an existing path.
In general, consider adding two anchor points for each curve along your path. Although you can create a triangular shape with rounded corners with just three anchor points, you have more control over editing that shape if you create three pairs of anchor points (six points total). Placing anchor points to form angles of around 120 degrees offers a reasonable balance between the number of anchor points and shape control.
When you want to create a curve coming out of a straight segment of a path, add an extra anchor point before the curve starts. Otherwise, the curve will affect the straight-line segment.