When I land in the first cell of the table I can navigate the table in NVDA using CTRL+ALT+Arrow Key of Direction I Wish to Go.  I remain constrained within the table if I try to use that key sequence in a direction that would take me out of it.  I can't remember the precise announcement, but it's quite clear that you're either at the first/last column/row of the table and you need to choose another direction.

        I have no trouble typing in any of the cells I land in.  If you have a table that's pre-formatted with either column headings and/or row headings you'll likely want to use the Set Column Headers and/or Set Row Headers command (see the section on Microsoft Word in the Commands Quick Reference), but perhaps not.  It depends on how well you know the structure of the table in question and how confident you are about knowing exactly where you are inside it.
 
        There is also an Add-On written by Joseph Lee, Easy Table Navigator, that allows you to create a "table layer" situation within NVDA such that when you invoke it you can simply use the arrow keys themselves to move within a table when that feature is on.   I just e-mailed Joseph about this add-on because the toggle that you use to change states is not defined by the add-on itself, but must be defined by the user.  He says you do this after you install the add-on by going to NVDA Menu, Preferences, Input Gestures.

          I asked for a copy of the template because I cannot imagine precisely why you'd be tossed out of a table when you attempt to type in a cell if you're in focus mode when you begin to do so.  If you're in browse mode heaven knows what might happen depending on what key you're pressing as part of the word you've started to type.

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Brian         Version 1703, Build 15063.296, Home 64-bit

 

     Travel is fatal to prejudice, bigotry, and narrow-mindedness, and many of our people need it sorely on these accounts. Broad, wholesome, charitable views of men and things cannot be acquired by vegetating in one little corner of the earth all one's lifetime.

            ~ Mark Twain