I tried a countif, but that still did not seem to work

the formula is the below, i have replaced the name below with %%%

=COUNTIF("[Book1.xlsx]Sheet1!$A:$A","%%%")

This does not work and comes up with this error -

The formula you typed contains an error.
- For information about fixing common formula problems, click Help.
- To get assistance in entering a function, click Function Wizard (Formulas tab, Function Library Group).
- If you are not trying to enter a formula, avoid using an equal sign (=) or minus sign (-), or precede it with a single quotation mark (').