What does the @JsModule annotation do under the hood?

Does it just run the side effects or can I somehow use it to import something the specified module exports? From the documentation:

and imports the JavaScript module file into the document provided to the browser.
I don’t understand what that means.

Side effects only. If you want to use imports you can create your own js/ts file, use imports from the other file and import your own js/ts using @JsModule instead

Thank you