Polylines are useful for drawing 2d schematic illustrations in Autocad. We show you how in our Autocad 2d courses. 
Polylines are groups of lines and arcs which act as a single object. For example, a box drawn using a Polyline will act as one object instead of four separate lines as opposed to creating a box with the Line tool. Polylines have properties such as thickness and curvature. They are good for creating schematic or symbolic illustrations like powerboards or electrical drawings, and when creating blocks – see another blog post on this topic.
To create Polylines you can select the Polyline tool, choose Draw > Polyline from the drop-down menu, or type PL in the Command line. To create a simple thick line, select the Polyline tool, click to specify a starting point, type W for width, type 2 > Enter, and 2 > Enter, and click to specify the next point. To change the width with the next segment, type W for Width again, and enter a new value. Keep clicking to continue the line, or click Escape or right-click > Enter to exit the command.
To create a large thick arrow, like in the screenshot here: select the Polyline tool and click on the screen. Then type H for Halfwidth > Enter. Then 10 for Start > Enter; 0 for End > Enter, click to establish the end point and click Escape to exit the command, or right-click and choose Enter.
For an arrow shaped like an arc, select the Polyline tool and click on the screen. Then type A for Arc > W or Halfwidth > 12 > 0 > Enter. Then click to establish the end point and click Escape to exit the command, or right-click and choose Enter.
The doughnut shape is ctreated using a different tool: select the Doughnut tool, or type DONUT > then 10 > then 20 > Escape.
To change the width of a line, type PE (Polyline Edit) in the Command line, select the polyline, type W for width and enter the new value. To create a schematic drawing or illustration set Snap and Grid to a certain value, eg.6 units, and draw with the Polyline tool. If you have an overlap of, for example, line and doughnut shapes, you can use the Trim tool to trim off unwanted segments.
We explore these features in full in our Autocad 2d classes. You can see many examples of our clients’ work on our Facebook page.
Other related Autocad 2d Blog Posts:

• Autocad 2d basics
• Autocad 2d introduction
• Autocad 2d drawing
• Autocad 2d workspace
• Autocad 2d isometric