It is especially visually clear on the DuckDuckGo site itself ... if you go to the site, type "!" in the search field, then say... start writing "reddit" you will see that matching "bangs" start filling the auto complete field below. However, the same search will work in the browser bar if you have selected DuckDuckGo as your default search engine. You need to use the bang, then the search term right after.
If you type "!reddit dogs" you will find yourself transported over to Reddit, with the built in Reddit search function showing a search for dogs.
If there isn't an existing "bang", it won't do it though. For example, "!prw tube mics" doesn't yield a PRW search, since no one has set that up (yet).
But this is the real super power of this search engine, in my opinion.