You can create a straight or curved line then customize it by changing its width (thickness) or color, or by adding different endpoints—for example, an arrow, circle, or square.
Do one of the following:
Click 
in the toolbar, then in the Basic category, click a line.
Options include a straight line with or without endpoints, or a line with editing points to create a curved line.
Select an existing line on a sheet.
To move the line, click anywhere on the line, then drag it to where you want it.
To change the line length or rotation, drag the white squares on the ends of the line.
For a curved line, drag the green dot to change the arc.
To see controls for changing the look of the line, click the Style tab at the top of the sidebar on the right.
If you don’t see a sidebar, or the sidebar doesn’t have an Style tab, click 
in the toolbar.
Click a line style at the top of the sidebar, or use the controls in the Stroke section to adjust any of the following:
Line type: Click the pop-up menu above Endpoints and choose an option.
Color: Click the left color well to choose a color designed to go with the template, or click the color wheel to open the Colors window and choose any color.
Thickness: In the field to the right of the color controls, click the arrows.
Endpoints: Click the Endpoints pop-up menus, then choose options to change the left endpoint and right endpoint.
You can change the look of the connection line, just as you would any other line, by changing its thickness, color, line style, and endpoints, and by adding effects like a shadow and reflection.
You can edit a curved line to add right-angle corners or curves. As you edit, you can quickly change corners to curves and vice versa.
Select the line, then click the Arrange tab at the top of the sidebar on the right.
If you don’t see a sidebar, or the sidebar doesn’t have an Arrange tab, click in the toolbar.
Click the Curve or Corner button in the Connection section of the sidebar.
If you don’t see the buttons, make sure you selected a line with an editing point between the endpoints.
To change the position of the angles or the curve, drag the green dot.
If you make changes to the appearance of a line, you can save a line as a custom object style.