Ads into post

Hi miknik. Which banner? In the single post? Home page? Other pages?

If you’re referring to the Featured Image, you need to set a Featured Image for the post, then set the post format to Image.

The easiest way to do that is to use a plugin. Here’s one made for Adsense by Google:
http://www.shoutmeloud.com/best-adsense-plugins-wordpress.html

And here’s an article that discusses several others:
http://www.shoutmeloud.com/best-adsense-plugins-wordpress.html