simply searching "shoes amazon" will do the job, or if I really want to search a specific site one can easily do "shoes site: amazon.com"
The search bangs take you directly to the search implementation of the site in question. Sometimes this is preferred to a Google search. If you try "!amazon shoes" on DDG and "amazon shoes" on Google, you can see the difference. Basically, in any case where you would type something into a site's search box (instead of Google's), it saves you a click or from having to navigate to that site first.