<head></head> section .Follow the 7 steps below to paste the code in the header of your theme in order to automatically insert code for Auto ads on all pages.
5 Step-by-step instructions:
1. Activate the ad inserter plugin. You should know how to do this, if you are using WordPress.
2. Go to the ad inserter plugin in your list of plugins
3. On the box shown, click on the last tab (gear icon 
– general plugin settings)
4. Click on the tab Header (for code in the <head></head> section)
5, Paste AdSense code for Auto ads into the code window
6. Click on the Enable button above code window to enable header code. I have problem in doing this first but to do that just click on the middle button where green light is shown in the picture below(green light must be on)
7. Click on the Save Settings button to save settings
This code will now automatically display AdSense ads on positions chosen by the code. Auto ads use Google’s machine learning to pick the best placements on your pages to show ads. You only need to add this piece of code to all your pages, and let Google take care of the rest.
It may take some time (usually hours) before it starts to serve ads because Google will check the page. However, if the ads did not show after sometimes and you have follwed the instructions above, and the code is properly installed, then check ‘Ads not displayed ‘ section for possible solutions.
NOTE:
The exact placement of ads will be done by the ad code, not Ad Inserter!
Source: blog.letgoonline.com.ng
