note input mode

Welcome Aboard... once you get the hang of note entry, it should go pretty smoothly.

Basically, for note entry:
1. Click on a rest or note (turns blue).
2. Press 'N' to enter note entry mode (or click on the Note input icon on the toolbar).
3. Select a note duration by entering a number - e.g. '5' for quarter note (or use the note icons on the toolbar).
4. Enter a note name (letter) or enter '0' (zero) for a rest.

OK... at this point you'll see that the blue highlight box moves to the right *and* the recently entered note is blue - that's because you have two choices:
1. You can modify the recently entered note.
2. You can continue on and enter the next note.

As you have mentioned in your post, for #1. - You can modify the recently entered note (the colored notehead).
For instance, here are some possibilities:
Maybe the note needs to be sharp (or flat) -> use the up arrow to add a sharp (down arrow for flat).
Maybe it needs to be placed an octave higher or lower -> use Ctrl+up arrow or Ctrl+down arrow.
Maybe you need to build a chord -> hold Shift while adding more notes.

If you don't need to modify the entered note, then you are at #2. You can continue forward and enter the next note.
This next note can either be of the same duration or of a different duration:

If the next note to be entered (at the blue highlight box) is of the same duration, just type the letter name of the new note (0 for a rest). It will then be added to the score and the blue highlight box will move on. Keep typing away until the note duration changes.

If the next note to be entered is *not* of the same duration, you must type a number (to change the duration - e.g. to '6' for a half note/rest) *before* you enter the letter name for the note. (BTW: When you type in a duration, the corresponding note duration icon on the toolbar is activated as a visual confirmation.)
So, if you have a succession of different note durations, you'll be typing: number/ letter... number/ letter... number/ letter... etc. (Of course, if a rest is involved it'll be number/ number because a rest is entered as the number zero.)

In summary:
In note entry mode, the blue highlighter box automatically moves as you enter notes.
You shouldn't have: to manually inch the blue highlighter on to every note with 'arrow' keys on (your) PC keyboard.

If you are *not* in note entry mode, and have a note selected (the notehead is blue) you can modify the note (make sharp/flat, etc.), but you need to use the left/right arrow keys to move backwards/forwards in the staff.

Regards.