The 3700 database elements seem to be a mess, but if you stare at them long enough, (I've been at it for 17 years), they start to make sense.
Tables that end in "def" are definition, or configuration, tables. Most of these are linked to the configurator in one way or another and can be updated through SQL using a non-dba login.
Those that end in "dtl" are mostly user transactions and are written to by POS operations or backoffice tools like PM or FM. These need dba access to edit, but you really don't want to be messing with these.
Tables ending with "ttl" hold accumulated totals, and are written to from the posting stored procedures. You also need dba access to edit these, and you also don't want to be doing that.
Another helpful thing to do is look at the relationships, (primary/foreign keys), for the tables. That will help understand how things are linked together.
There are two report templates loaded with the 3700 that aren't in the report list, but can be really helpful if you open them in Crystal - Schema.rpt and Domain.rpt. The first will diaplay the entire database schema, and the second diaplays all the custom data types and some will have a definition for the codes they use.