Too often, developers produce database documentation containing just a schema information - table and column names, without any descriptions. See a few examples.
Database Comments Articles
Most popular database engines provide option to provide descriptions for schema elements. This article shows how to check if your database uses them.
Quick tutorial on how to view and edit table and column comments with MySQL Workbench.
Quick tutorial on viewing and editing table and column comments in free Oracle SQL Developer.
4 options you have to edit column descriptions in SSMS and 2 for describing tables.
Overview of capabilities of commenting objects in Oracle database.