Sum

Add up the values in a query result set. (SQL).

Syntax
      Sum (expression)

Key
   expression   A field or formula that evaluates to a numeric expression.

Use the Sum function in the access query builder by clicking the Totals toolbar button:

Σ

The Sum() function is used in conjunction with the Group By clause.

Example

Select Sum(price) 
from T_Sales 
Group By Supplier;

“Winning takes talent; to repeat takes character.” ~ John Wooden

Related:

DSum - Return the sum of values from a set of records.
Avg (SQL) - Average
Count (SQL) - Count records
Max (SQL) - Return the maximum value from a query.
Min (SQL) - Return the minimum value from a query.
Partition (SQL) - Locate a number within a range.