. denotes a css class and # denotes an id
css pseudo classes include :link, :activated, :hover - there's other ones too
precompiling assets creates a folder in your public directory with assets precompiled. they will then override your app/assets. running rake assets:clean will get ride of them. rake assets:precompile will precompile them. good for heroku because ?
 'as' is used in route helpers to rename your url helpers, to lets you specify controller and action in the form: 'controller#action ,  you can also you controller: controller_name, and action: action_name to be more specific