I think that is pretty much spot on. By default, Rubygems will add the lib directory to the loadpath, but you can push any directory you want onto that using the $: variable. i.e.
$:.push File.expand_path(File.dirname(__FILE__) + '/../surfcompstuff')
That means when you have say, surfer.rb in that dir, you can require "surfer" anywhere and the file will be found.
Also, as a convention, classes and singletons get a file and modules get a directory. For instance, if you had the LolCatz module and the LolCatz::Moar class that would look like:
lib/
appname.rb
lolcatz/
moar.rb
That is why there is an lib/appname folder because most libraries are in the appname namespace.
Additionally, if you try running the command newgem --simple [projectname] that’ll quickly generate a scaffold for you with just the bare essentials for a Ruby project (and by extension a Ruby Gem). There are other tools which do this, I know, but newgem is pretty common. I usually get rid of the TODO file and all the script stuff.