"Channel" is the term used to refer to the individual entries that make up the portal. Each channel has its own section of the portal window, with a title and a row of control buttons, beneath which specific information or an application appears (weather, news, search, reports, links or bookmarks, etc.).
You can subscribe to channels that interest you (see How to add entries) and unsubscribe from ones that you do not wish to see (see How to remove entries). You can place channels wherever you wish in your portal window, in any column under any tab.
A tab is a layout of a group of channels. Just as a section of a newspaper contains stories which logically may be grouped together, a tab often contains channels which have a common theme.
The top left part of your portal window should show a group of tabs, with "Cornell" at the left and "Personal" at the right. You can change and rearrange the channels in these tabs to suit your needs and preferences; you can also delete tabs or create your own. (Warning: You can't get tabs back once you delete them.)