We have a lot of shortcodes for you to use. Read the description of all the shortcodes so you can find the one you want to use:
http://www.tipsandtricks-hq.com/ecommerce/wp-estore-shortcodes-and-functions-reference-460
When you have found the shortcode(s) that you want to use, simply add a standard “Text” widget to your sidebar and use the shortcode(s) in it.