You need to use the cdp utility that is part of trs2004. I moved the files that I wanted to package into the my trains folder in the custom section. Then it was a matter of selecting each file to make/package its own cdp.
This is a strange question, because if it is your content them you would have made it. You would have needed to copy the files to an appropriate subfolder in the Custom folder for Trainz to recognise it. So that's where it would be.
To make a .cdp file use ContentDispatcher program which is the cdp utility referred to by rgcx above. It is found in the TRS2004 directory.
If you click on a file with a .cdp extension (suffix) then the package is installed in Dispatcher\Downloads folder with a file named after the kuid of your content.
You may not upload content made by other users. Only content which has your own kuid number. If you modify another user's content it should only be uploaded with the author's permission.