Allow all access to database files (dumb newbie question)

[Harry G]

I am running database program as a user. I have another user on the same 
computer I want to give access to the database file, and also a bunch of 
documents.

Where is the best place to put this in the filesystem?  I see a lot of places 
that might work, but I want to do this properly.  Both users will need read 
and write access, by the way.

TIA

Harry G