In Access, tables don't perform calculations. Tables store data. Queries,
forms, reports, data access pages, macros and VBA code perform calculations.
In a query, you would use an expression such as ...
MyProduct: [MyField1] * [MyField2]
.... where 'MyProduct' is whatever name you want to use for the calculated
column in the query, and 'MyField1' and 'MyField2' are the names of your two
fields.
In the Control Source property of a text box on a form or report you would
use a similar expression ...
= [MyField1] * [MyField2]