Matched Content is a free service that promotes relevant content from your site to your site's visitors, and can help to increase your page views and the time your readers spend on your site.
To create a new Matched content unit:
Step-1. Sign in to your AdSense account.
Step-2. Click Ads 
Step-3. Click By ad unit.
Step-4. Select Matched Content.
Step-5. Use the drop-down in the upper corner of the preview area to see
which of your sites are eligible for Matched content.
Step-6. Give your Matched content unit a name.
Step-7. In the "Style" section, change the style of your Matched content unit to match your site.
Step-8. In the "Size" section, choose an ad size that fits your layout.
Step-9. In the "Ad options" section, leave Monetize with ads switched on unless you'd prefer not to show ads in your Matched content unit.
Step-10. Click Save and get code.
Step-11. Copy and paste the ad code into the HTML source code of any of the pages on your approved site.