The editing area is a standard GTK editing area. This means there are many keyboard shortcuts available to navigate through the text.
Ctrl-Right-Arrow will jump to the next word boundary
Ctrl-Left-Arrow will jump to the previous word boundary
End will jump to the end of line
Home will jump to the beginning of the line
Page-Up will jump one page up
Page-Down will jump one page down
Ctrl-Home will jump to the top of the document
Ctrl-End will jump to the end of the document
These shortcuts are also available when selecting text. Some examples:
To select the current line, press Home, hold Shift and press End.
To select the current word, press Ctrl-Left-Arrow, hold Shift and press Ctrl-Right-Arrow.