I have heard that "Excel is to game designers what Microsoft Visual
Studio is to programmers" -- and as a relative newbie, I'd like to
learn howso.

One common thing in game design is branching and recombining plots (or
story elements). I can break up the plot into least-units, and put
each unit in a cell. But beyond that, how can Excel help with this? My
problem is that sure, I know what I know, but I can't imagine what I
don't know.

So for example, I know I can color the "key plot element" cells, then
sort them by color so I can see all the "key plot element" cells
together. But I don't know how to use Excel as a plot-analysis tool.
"How will a given design play?" and "where are the stubs in the
story?"

Should I somehow flag certain cells with a set of keywords, then write
a macro which automatically re-orders the cells in an instructive way?
Is this the sort of thing that "Excel is to game designers" means? I
think maybe I'm missing something simpler.

Another problem: inventory being a primary way of solving puzzles, the
idea apparently would be to use Excel to track the puzzle-solutions a
player may have available (pick-up-able) and ready (in inventory).

Can I associate plot points with game-objects which become available
at that point? Then, can I pick a plot point and get a list of all the
game-objects available at that point? (Corollary: can a plot point
remove an item from the list of available objects?)

I'm sort of wandering in the dark here. Not sure what questions to
ask. Of course I looked all over online, but discovered nothing
apparently interesting. If you have any general pointers on this
topic, I'd love to hear!