In B2 on the destination sheet enter & copy down:

=SUMIF(Sheet1!A:A,A2,Sheet1!B:B)

Replace Sheet1 with the name of your source sheet.

Gilbert De Ceulaer wrote:
How do I do this ?

I have a datebase in one sheet.
In column A are names, let us say of products; they are NOT unique, and NOT
sorted.
In column B there are numbers, let us say amounts.

In another sheet, I want to know the total number for the different names.
In column A are the names, unique in that sheet, but not necessarily sorted.
In column B I would like to have the total of the numbers corresponding to
that name from sheet number one.

As normal, I already tried several possibilities.
Gilbert De Ceulaer