If you have a mouse with a scroll wheel, you can use the wheel to scroll up and down in the text area. Various modifier keys change the action of the wheel:
Shift - moves the horizontal scrollbar.
                time.
Control - scrolls a single line at a
                time.
Alt - moves the caret up and down instead
                of scrolling.
CTRL+SHIFT - scroll a page at a time. 
Alt+Shift - extends the selection up and down instead of
                scrolling.
Keyboard commands for scrolling the text area are also available.
>> (shortcut: C+e C+j)
        scrolls the text area in order to make the caret visible, if necessary.
        It does nothing if the caret is already visible.
>> (shortcut: C+e C+n) moves
        the caret to the line in the middle of the screen.
>> (shortcut: C+QUOTE) scrolls the
        text area up by one line.
>> (shortcut: C+SLASH) scrolls
        the text area down by one line.
>> (shortcut: A+QUOTE) scrolls the
        text area up by one screenful.
>> (shortcut: A+SLASH) scrolls
        the text area down by one screenful.
The above scrolling commands differ from the caret movement commands in that they don't actually move the caret; they just change the scroll bar position.