Can anyone tell me how exactly to use this row -> key, select key coloumns option in Edit Check dialog box.

Winrunner help says "Key: WinRunner looks for the rows in the selection according to the data in the key column(s) specified in the Select key columns list box. A shift in the position of the rows does not result in a mismatch. If the key selection does not uniquely identify a row, WinRunner checks the first matching row. You can use more than one key column to uniquely identify the row."

Can anyone give me clear idea/or good example of this pls...