menu from this example was created with Quick BD Menu (http://www.dvd-logic.com/quickbdmenu
). This means all navigation commands were set automatically. So, you do not need to see so deep on commands as thay are a little complicated due to special mechanism used by Quick BD Menu that allows user do not think about navigation commands at all. Quick BD Menu allows you just set numbers of audio/subtitles streams and chapters number and you will receive Interactive Menu file (*.ies).
However, here are some detailed explanation:1.
You should have same blank streams number in "Top Menu" if you are using menu after Quick BD Menu. That allows automatically operate with streams in menu.2.
Yes, you can use any "empty"/"blank" streams.3.
Move  1 means to store value "1" in register 2. It has no special sense for you, this is just internal work after Quick BD Menu.4.
SetStream refer to current position, so, for example, if you have Title1->MovieObject1->SetStream->PlayPL MainMovie then this is for MainMovie. Command "SetStream ShowPG_textST:On PG_textST:1" turns on subtitles stream 1 by default.
Hope this helps.
And sorry for my English too.Best regards,