The panels in GNOME are the little bars that are on the bottom (and sometimes top, or even on the sides) of your desktop. Think of them like the Windows taskbar on steroids
Panels can have all kinds of things on them, like launchers, clocks, volume control, window switcher buttons, and things of the like.
Adding things to a gnome panel is easy. Just find some empty space on the panel you want to add to, right-click on it and go to "Add to panel." A list of all kinds of things comes up. Click on what you want to add and click on the Add button (will have a plus sign next to it.)
If you want to get rid of something on a panel, right click on what you want to remove and click on "Remove from Panel" (has a minus sign next to it)
Deleting/Adding new panels is also just as simple. To delete a panel, find some free space on the panel you want to delete and click "Delete Panel" (It'll have a garbage can next to it) To add a new panel, right click on free space on any panel and click "New panel" (will have a plus sign with a piece of paper)
HTH, and welcome to the Linux community!