If you are trying to pull information from one cell of the source sheet to
one cell of the destination sheet, then that's what you've got. It should
look something like:
='[Sourcebookname.xls]Source sheet name'!A1. If it includes $ signs for
absolute addressing, such as $A$1, then you probably want to remove those if
you want to copy the formula to other cells as below.
Having ensured that you've got relative rather than absolute addressing,
then if you wish to do something equivalent for other cells on the sheet,
then merely copy your destination cell across as many rows and column as
applicable.
If you are trying to pull information from a range on the source sheet to a
cell in the destination sheet, then when you've instered an appropriate
formula in the destination sheet you can select the relevant range from the
source sheet, such as:
=AVERAGE('[Sourcebookname.xls]Source sheet name'!$A$1:$D$8)