Tab will move the highlight bar down (and Shift-Tab up) to the next entry at the same level of indentation, jumping over all entries at a lower level and stopping whenever it comes across an entry at a higher level.
The left-arrow and right-arrow keys are useful for moving between levels. Within a given main (1st level) directory, the right arrow moves down one sub-directory at a time, but will not proceed to the next main directory. The left arrow, in contrast, will move up to the parent of the current directory each time it is pressed. But it stops at the main directory; to go to the root, use the Home key. And to go to the very bottom, use End.
Tom Ruben