What does it mean to "use the Content-Disposition header"?

[awdm]

The documentation says that for a file received from a remote server, one should "first try to use Content-Disposition attachment response header". But a header ist just some meta info, not a function I can call. If I follow the link, it explains what information the header contains, but still doesn't provide any clarification.

So what exactly is meant with "using the header"?