As the title says, can't find any documentation on what @something does in rvm use 2.0.0@something?
RVM is the Ruby Version Manager and its website is here: https://rvm.io/
The command rvm use 2.0.0@something tells RVM to change the setup of your current shell (terminal) so that you are using ruby 2.0.0. It also says to use the gemset named something. Gemsets are a feature of RVM that let you segregate your Ruby gems into different sets.
More information about gemsets is here: https://rvm.io/gemsets/basics