Joomla! Documentation™

You can use Google AdSense without installing an extension. Using AdSense requires the following steps:

1. Create a Google user Account and follow the instructions for creating your AdSense settings. In the end you will have a chunk of JavaScript. Copy the script and save it into a file for later use.
2. Log on to the back end of your website with an Administrator account.
3. Go to Site > Global Configuration and change the default WYSIWYG editor to 'editor – no editor'. If you don't change the default editor to no editor the WYSIWYG editor will change the JavaScript, even if you edit the HTML source.
4. Go to Extensions > Module Manager and create a new module instance of module Custom HTML.
5. Paste the copied JavaScript into the custom output and fill in the other parameters like title. Save the module instance.
6. Go to Site > Global Configuration and change the default WYSIWYG editor back to what it was.

There are a lot of extensions for implementing Google AdSense (see the Google Ads section of the Joomla! Extensions Directory. Maybe some of them can be useful if you have specific needs. But if you just want to use AdSense as it is, you don't need them.