Hi, I think it might be a very simple problem, but I can not find resources addressing it.
Normally when we want to create some file, say a docx, we right click inside lister and context menu pops out, we choose "New" item (I am not sure if it is exactly this, coz my UI is in Chinese. Just the item that is entry to create all sorts of new type of files), and we click the subitem "New word docx..." (you get the meaning).
What are the codes to create a button that when clicked, popping out all these new types of files for user to choose from?
Thanks!
If you want buttons to make individual file types, see the post linked above.
If you want a list like the right-click New menu, it's part of the default toolbars, in the New Folder button's menu:
You can edit that menu to get the command that generates it if you want to put it somewhere else.
I want this, what your saying "You can edit that menu to get the command that generates it if you want to put it somewhere else." is exactly what I cann't do. 
Thanks for the quick response, though I want a list like options, but your reply gives valuable content.
I can edit the normal button, but this one seems tricky. When in edit mode, the original item list changes from
to
And, although I seem to manage to locate the code that is responsible, I think is:
Marker MENU=File
When such button is created, and edit mode exited, the button automatically hides.
That's a completely different menu. Edit the one I showed in my screenshot, that is part of the New Folder button-menu.
Solved it like a breeze. 
My fault, I customized menu too much and I put that one to a nested location which is so hard to notice. Thanks!
I am following your directions regarding getting access to these menu items while in the customize lister mode, but when i am in this mode, that menu item for "new" doesn't have the arrow, its only a button, and I cannot access the items within that menu. I am looking directly at the default toolbars under the customize menu. What am I doing wrong?
You're doing nothing wrong, it's normal. That sub-menu is built dynamically from the command of the button (FileType NEWMENU : NEWMENU is indicating to build the submenu).
If you want to have a button dedicated to a specific file type, you need to follow the instructions in the link I provided above where you specify the type, for instance FileType NEW=.txt). Look at this post for further options and descriptions.
Bruh,
You are pretty darn great. Thank you for your insanely prompt response time. Opus should put you on their emergency response team lol! 