Adsense code

Hello i applied for adsense and i got the code i need to insert before they review the page. Where do I need to insert it?
Do i need to insert it in header.php or in ads section in theme panel?

I placed the code there but i get a second reject from adsesne. I dont know why. Where did i get wrong?

Your AdSense application status

As mentioned in our welcome email, we conduct a second review of your AdSense application once AdSense code is placed on your site(s).

We did not approve your application for the reasons listed below

Insufficient content: To be approved for AdSense and show relevant ads on your site, your pages need to have enough text on them for our specialists to review and for our crawler to be able to determine what your pages are about.

To resolve this issue, please work through the following suggestions:

Make sure that your pages have sufficient text – websites that contain mostly images, videos or Flash animations will not be approved.
Your content should contain complete sentences and paragraphs, not only headlines.
Ensure that your website is fully built and launched before you apply for AdSense – do not apply while your site’s still in a beta or “under construction” phase or only consists of a website template.
Place the ad code on a live page of your website. It does not have to be the main page, but test pages that are empty except for the AdSense ad code will not be approved.
Provide a clear navigation system for your visitors so that they can easily find all of the sections and pages of your website.
If you’d like to monetize YouTube videos, please apply for the YouTube monetization program. Note that blogs and websites that contain only videos will not be approved.