You have several ways to combine two open paths into a single path.
To join two open paths
Select the paths you want to join.
Do one of the following:
On the Object menu, click Join Path (or press CTRL+J).
Right-click the selected paths, and then click Join Path.
Microsoft Expression Design moves the two end anchor points that are closest to each other to a position halfway between the two objects.
Using the Direct Selection tool, select an endpoint on one path, hold the SHIFT key while you select an endpoint on the other path, and then press CTRL+J.
Expression Design joins the two points that you selected
To join the remaining open ends, select the path object, and then on the Object menu, click Close Path (or press ALT+J).
You can also join two paths with the various drawing tools, as long as the Drawing tools append to path option has been enabled.
To enable the Drawing tools append to path option
On the Edit menu, point to Options, and then click Stroke.
On the Stroke pane, under Stroke, select Drawing tools append to path.
To use a drawing tool to join two paths
From the Toolbar, select the Line, Pen, Polyline, B-Spline, or Paintbrush tool.
Begin drawing over the starting or finishing point of the first path and then end your drawing over the starting or finishing point of the second path.
When you use the Paintbrush tool, you must hold down the ALT key when you start and finish the line. However, you do not have to hold down the ALT key when drawing between the two points.