Whichever section of the CAD menu systems (shown above) you use, it is fairly straight forward to draw the road marking. You need to select a marking from the menu, then pick a series of points on the screen, and the marking will be added to the drawing. The GuideSIGN Markings menus could be considered as a vast collection of buttons, each one drawing a different road marking. When you select the button, a text prompt will be displayed on the command line (and sometimes next to the cursor) indicating which points to pick and in which order.
You will find that most buttons will draw markings in similar ways, although there are some buttons that will be more complex and result in more complex markings. Hopefully the text of the command prompt will guide you through the steps and ask questions for any choices that need to be made.