Essentially, you have to find a place, where you want your banners on. For example, if it’s just an img banner and you don’t wanna count clicks,
- upload your image to your WP,
- copy the direct link to img,
- go to widgets, choose Text Widget,
- paste this code inside the box:
<a href="[link for ad purposes]" title="[your special title for that ad]"><img src="[link to image]" alt="[your alt text]" /></a>
There are plugins and widgets for ad placement, for example Woo Adspace Widget (they include it to their themes). Check Woo Themes site.
Also you may use Custom Fields (advanced technique).
What is “468×60 adsense code” & how do I input it?
Adsense code is what google gives you, if you have an account in their system. Registration is needed.