Once Google approves your blog for Matched content, you can start generating Matched Content unit from your Adsense account. By placing the code of the matched content unit on your blog, Google will be able to display relevant articles (below your blog posts) to visitors of your site based on topic similarity.
To create a new Matched content unit:
==> Sign in to your AdSense account.
==> Click the "My ads" tab.
==> On the sidebar, click "Content".
==> Click +New ad unit.
==> Give your Matched content unit a name.
==> In the "Ad size" section, choose an ad size that fits your layout. Automatic Size (Responsive) recommended!
==> From the "Ad type" drop-down, select "Matched content" only.
==> (Optional) In the "Text ad style" section, apply a style for your Matched content unit.
==> (Optional) Set up a custom channel to track your Matched content unit. Learn more about custom channels.
==> Click Save and get code.
Copy and paste the ad code into the HTML source code of your approved site.
Google recommends that you place your Matched content unit directly below your article (below the fold), and either above or below an ad unit.
While your Matched content settings are propagating across Google systems, standard ads may serve in your Matched content unit. To avoid this, please wait 15 minutes before putting this code on your site.
For best results, Google recommends placing your Matched content unit directly below the article (below the fold) and either above or below your ad unit. When placed directly above or below an ad unit, Matched content units can improve the visibility and engagement rate of your ad units.
NB : Matched content units don't count towards your Google content ad limit per page.
Recommended: How To Check If Your Blog is Approved For Adsense Matched Content