how to subtract two column from multiple tables

If I understand your question correctly, you need to create a query where you join the tables. After doing that you can do the calculation.

Consider the following example

SELECT t1.A,
       t1.B,
       t2.C,
       t1.A - t1.B - t2.C AS Calculation
FROM Table1 t1 INNER JOIN Table2 t2
     ON t1.ParentColumn = t2.ChildColumn

For more information about the joins, have a look at Visual Representation of SQL Joins[^]

ADDITION

If this is to be an update situation for for example Table1.D then consider the following example

UPDATE t1
SET D = t1.A - t1.B - t2.C
FROM Table1 t1 INNER JOIN Table2 t2
     ON t1.ParentColumn = t2.ChildColumn

For info about using joins in update statements, see UPDATE[^]
Another variation could be for example

UPDATE Table1
SET D = (SELECT Table1.A - Table1.B - t2.C
         FROM Table2 t2
         WHERE Table1.ParentColumn = t2.ChildColumn)

Note that this must return only one value per each row in Table1 so if the relation is one-to-many you need to restrict the query or use aggregates such as SUM