How to host files downloaded from server?

Countless times I’ve tried to get a certain addon working and it won’t work, either because I’ve placed the files in the wrong place or they’re the wrong files.

However, when I join servers that clearly work, I download their files.

Where are these files stored, and is there a way I can use those exact files to host my servers, as I know they work?

You mean certain files that you want clients to download arnt downloading?

Nope, I mean that when I join a server, I download files. These files obviously work and are used by the server.

As I also downloaded them when I connected, can I not use them when hosting my own servers?