You can create paths using path tools.
To continue drawing an existing open path, select the Bezier Path Tool or Freehand Drawing Tool and click the cursor over either end of the path.
Working with Paths
Drawing Straight Segments Using the Bezier Path Tool
Drawing Curved Segments Using the Bezier Path Tool
Drawing Arcs Using the Bezier Path Tool
Drawing Segments Using the Freehand Drawing Tool
Converting Objects into Paths
Converting Stroke to Outlines
Selecting Points and Segments
Using DesignCentral to Edit Points and Segments