Basic Question: Max file structure?

That sentence you quoted leaves out an important factor. The abstraction file must be in a place where Max can find it: either in the same folder as the parent patch, or in a folder that is part of the Max File Search Path.

Max Tutorial 15 Abstractions says, "As long as your abstraction can be found in the Max file path, you can type its name into a new object box and it will be loaded directly into your patch. The abstractions used in this tutorial are in the same folder as the patcher accessing them; a library of abstractions can easily be created by placing them in a folder (or a bunch of folders) inside the "patches" folder of your Max installation, or anywhere else Max looks for files."

The tutorial you're reading does say, 'Save the patch as "add60.maxpat" into a Max folder,' but that's not really as specific as it should be. You can solve the problem by saving your newly started patcher in the same folder as your abstraction file before you create the object in the new patcher, so that your new patcher now exists in the same folder as the abstraction file, or you can simply save your abstraction file in a folder that you know is included in your Max application's file search path.