Create Slide
The 
The slide file must have the same name as the block that it represents. If a block is selected that does not have a corresponding slide, a preview will not be shown in the dialog box. The block will still insert properly if a corresponding slide does not exist.
To create a slide, go to
Ribbon: 
Pulldown Menu: 
Save Slide As Dialog Box​

Specify the name of the slide file to create, then press the button to create the slide.
You will be prompted to draw a box on your drawing. A snapshot of everything inside the box will be saved in the slide.
Specify first corner of slide:
You will then be asked to specify the opposite corner of the box.
Specify second corner:
The screen will flash while the slide is being created.