One way to create a subscription list is to export an OPML document from your feed reader and open it in the OPML Editor, exactly the same way you'd open a document in a word processor or a spreadsheet.
You can choose the Open command from the File menu, or drag and drop the file icon on the OPML Editor application icon.
To create a new one, choose New from the File menu, enter the feeds you want to subscribe to and save the file to disk.
As its name implies, the OPML Editor is designed to edit OPML files. It opens and saves them the way any application would open and save its native file type.
In addition, you can use the Open URL command in the File menu to open an OPML file over the net, if you know its address.