Not sure what you mean by "interact". Perhaps 'pvp', 'chest-access' and/or 'use'? See http://wiki.sk89q.com/wiki/WorldGuard/Regions/Flags Ask if you still need help.
I believe that WG has block 'break' and 'place' flags that can be set.... look through the wiki page for the appropriate flags and set them for your region.
If you simply define a region and make yourself the owner, no one else will be able to place or break blocks in the region. No other flags are needed.