Okay, I should read my own manuals before replying...
Yes, the desc. is optional. At some point in development it wasn't
Placement of lib files is a bit confusing. But I think it is explained in the lib section in the "Paths, Files" section of the manual. But, to summarize: if you want to put a lib file in any location other than stdlib you need to either use the "USE" directive or set the location of YOUR files with "SetAutoLibPath" command.
Both USE and SetAutoLibPath are relative to the base LIB directory, so it's not too complicated as to long path names.
The reason for this is simple: you can have your own, parallel, set of grooves this way. Your install is fine.
Have a read over the manual section and I think it'll make more sense.
Again, shout for more info.
And I'm glad you are having fun with MMA! And I look forward to the ideas, grooves, etc you will share with the rest of us in the future!
Bob.