press on the home SCREEN (empty spot on the "desktop"), and a menu will pop up.
holding the home BUTTON will open a list of your 6 last used apps. makes it easier to jump between a few things quickly
they're things that are designed to give you information without having to open an app
like the calendar widget will show your agenda without having to open the calendar, you can download weather widgets to show you the weather, music widget can control your media player without opening the media app, the picture frame just adds a personal touch, etc.
you can find more in the marketplace as well.