Whether you're looking to sell advertising space on your website or promote your own activities, you need to understand how the Joomla banner feature works. This can be daunting for beginners so here is an overview of the process:
1. Create your banner(s) and upload them (using Media Manager or FTP) to your "images/banners" folder
2. Create at least one banner category - "Components - Banner - Categories"
3. Create at least one banner client - "Components - Banner - Client"
4. Create your banner(s) - "Components - Banner - Banners"
5. Create a module to display your banner(s) - "Extensions - Module Manager - New - Banner" and assign it to your desired template position.
This works well, but it only displays basic statistics and there is no automation. If you are serious about making money from your website, you will quickly outgrow the standard banner component.
If you are displaying banners, or if you have never considered displaying banners, I recommend taking a look at Ad Agency by iJoomla. This comprehensive extension includes all the features you need to create different types of banners, sell ads and monitor results. If you have a website running Google AdSense, you really should switch to running your own banners. One publisher went from making $178 a month with AdSense to almost $3000 a month by using Ad Agency.