"We've provided CSS..."- this is not clear

In app/views/tags/index.html.erb at line 12, iterate through each tag in the @tags array. Then for each tag, display its title and image. 
We've provided CSS in app/assets/stylesheets/application.css.

What does that last sentence mean? Copy the whole of the CSS file into tag.css? Or does the index.html.erb file already link to application.css?

Once I've sorted that one out I'll have another go at the file: it gets marked correct, but it displays no data.


All you have to do is what the first line asks you to do. The second line can be ignored.
Just iterate through the tags with the @tags.each do |t| line in the HTML.

The CSS part just means that the page will come out styled because they added some code to do that, which you didn't write, so they're telling you not to be surprised when it comes out with pretty images and things.