"database from a third party company. I do not know what it is based on but it looks like a very simple one in VB."
Let's start by correcting things - NO database is "IN" VB.
VB is a development LANGUAGE which can use various 'backend' databases.
SQL Server - 'standard' or 'express' (most often used)
Next, while, if you have the appropriate Database security rights, you can indeed make changes to the data tables within the 'backend' database - either new tables and/or new fields in existing tables, that alone does not make those new entities appear to be viewed and/or used within the application's GUI interface (entry forms, etc.)
NOTE - if you were to make these changes you need to be very cautious because some changes could 'break' the existing data table referential integrity and thereby render the application non-functional.
A very few applications are 'intelligent' enough to dynamically recognize 'backend' data table changes and automatically reflect those changes and/or enable them to be incorporated into the applications GUI interface.
Due to the nature of the changes you describe, your best bet in this instance would be to have these changes made by either the application vendor itself or by a software contractor who has a LOT of experience in that particular application.
Suggest you copy this entire environment to another machine that cannot even "see" the original. Then experiment away as long as your work is completely isolated and Nothing can "bleed across" to the original envieonment.
One of the first orders of business will be to determine the underlying data structure(s).