1.It's a test that simulates a browser accessing our application.
2.The "erb" stands for "Embedded RuBy". .erb files look like about.html.erb and live in the "views" directory.They are just html files with embedded ruby in them.
3.Ruby complains if we try to evaluate an undefined local variable, but issues no such complaint for an instance variable; instead, instance variables are nil if not defined
4.The @ indicates that this is an "instance variable". An instance variable defined in the action (or function) of a controller is automatically available in the view of that same name.