Joomla! has already a native component dealing with banners and pretty much it does the job. But if you need more than that, you have to use a more sophisticated solution like Google ad manager, aka Doubleclick for Publishers (DFP).

Step one - Setup Google ad manager

Sign in with your Gmail account and go through the quick start guide to setup your first campaign.

Step two - Google ad Manager module

Download and install the Google ad Manager module (comes along with a plugin) from Joomlaworks website. On the module parameters enter the correct details for "Publisher id", "ad slot" and there you go, publish the module and enjoy the benefits of the Google Ad Manager Service in your Joomla! website.