While working with Dynamics 365 CE, I’ve run into similar issues. Here's what I've learned from my guess work:

Field Descriptions Within Dynamics 365 CE

Field descriptions may be located by navigating to:

Advanced Settings > Customizations > Customize the System > Entities > [Your Entity] > Fields Click on any field and find its description (if provided by the admin or developer).

Backend Database Identification

Online version: Operates on Dataverse (formerly Common Data Service).

On-premise version: Generally uses Microsoft SQL Server.

Viewing Queried Tables
With tools like XrmToolBox (and especially its plugins), Metadata Browser or FetchXML Builder, you can view entities/tables that are queried.

Also, look at Plug-in Trace Logs, and telemetry through the Power Platform Admin Center.
Dynamics-Created Tables That Aren’t in the Backend

Certain system tables are virtual or hidden: they exist in the app but not the physical DB.

Use the Dataverse Web API, the Power Platform SDK, or tools like Solution Explorer to access these hidden resources.

Column Descriptions & Business Context

In case you need some very specific descriptions from the system's columns, consider using the XrmToolBox's Metadata Document Generator.

It also permits the exporting of data types, descriptions, and other meta data which is ideal for documentation or even analysis purposes.

If you hope to have a more comprehensive architectural understanding of Dynamics 365 and how it is implemented in practices, I found this breakdown helpful:

Microsoft Dynamics 365 Services — it provides a fundamental learning point, more so for those straddling the technical and business sides.