A SHORT press of the PAGE key brings up the SD card browser page:
This allows you to browse the SD card contents. On each file or folder, pressing ENTER will bring up a contextual menu with some basic file operations (copy/delete), as well as others depending on the file type.
See the SD Card for more details on the conents of the sdcard.
The microSD card can be formatted by selecting the relevant option in the menu that appears when pressing MENU LONG. A confirmation will be required.