The banner plugin is part of the core plugins, but you need to install it at first (it was active by default in the older version).
You can add banners to your site 2 ways in version 2 (there was only one way in the older version).
This way is limited and it needs to be supported by theme (of course, if you use shortcode menus, you can use menu manager)
Add banner menu to desired menu area and don't forget to set its configuration (otherwise nothing is displayed)
The banner plugin gives you the option to not only sell banner space for a specific amount of time but also by the number of times a banner has been clicked on (selected) by the viewer.
In banner administration just add a new banner, select campaign. All fields are intuitive,