How I can scan all rows of the datasource?

How I can scan all rows of the datasource?
How I can move at the first row of the datasource?
How I can move at the next row, the last, the previous...
It's the reporting designer of Visual Basic .Net.
I would like to scan all rows to find an element or to do an operation, ...
Thanks.

Huh? I didn't get the point.
Mira, si eres de un país de habla hispana escribe tu pregunta en espa?ol; tal vez pueda ayudarte.

|||Reporting Services is not a programmatic / cursor method of accessing data. The rows of the query results are processed by evaluating the expressions in the report definition. Your operations are included in these expressions (e.g. =Fields!A.Value - Fields!B.Value).