Design > Blocks
First you need to create new Banner using Design > Banner manager
Then create new block with Banner type. Go to Admin-Design-Blocks and click the INSERT button, select Banner block Tab. Fill the following fields:
Custom Block Name: block name visible in Admin > Design > Layouts
Custom Block Title: name shown on Storefront
Use block wrapper (appearance): recommended value is Automatic
Use block's frame: set ON to display frame
Custom Block description: internal use only - not required
Banner Group Name: Select banner group to display: banners and banners groups can be added at Admin > Design > Banner Manager
Selected banners: Select banner to display: banners and banners groups can be added at Admin > Design > Banner Manager
Go to layout for product details page Design -> layouts. Locate where you want block to show, select block and save.
If You look how to edit Main page Banner Slideshow please read this manual.
Short YouTube video about banner bock management in AbanteCart.