What file to edit to create meta tags content and keywords?

[surflook]

What file would I edit to put my websites meta tags (keywords and description) to make it search engine friendly? Is it the index.php file? What would be the best file to put the meta tags once the site is finished and moved to the root directory so the root (sitename.com) is se friendly and indexed well? Also... when I set up wordpress it asked a question "do you want your site found by search engines?" and I said no since I do not want the directory indexed while I am building the studiopress wordpress site. Is there a way to go back to that and choose Yes later?