How do I add meta title/description and intro text to a Channel index page?
From the docs:

Singles

Singles are used for one-off pages that have unique content requirements, such as:


home page
an About Us page 
a Contact Us page


Unlike the other section types, Singles only have one entry associated with them, and they don’t have an editable Author, Slug, Post Date, or Expiration Date.



So create the fields you need, create a new single for your index page, add the fields to the single, set the single to load your index template, then code your new fields into the template