Just below the panels are 4 icons in the Dock area. While you can switch between panels, these icons stay in the Dock unchanged to offer you a quick access to some of the frequently used apps.
The maximum icons you can have in the Dock are only 4. And the trick to have more icons in the Dock area is to group apps into a folder, and then place the folder in Dock area.
For my example, I will group all the web browser apps, which I used interchangeably into a folder named Browsers.
Then move the folder into Dock area to replace the Internet icon.
Now, by tapping the Browsers folder, I will get more icons.
(Find a list of tips and tricks for Samsung Galaxy S3 and Android here.)