As brother thargas has explained, you need to look at the documentation. Type perldoc File::Find and you'll be presented with an example in the Synopsis section that should answer your question:

use File::Find;
find(\&wanted, @directories_to_search);
sub wanted { ... }
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You pass File::Find::find two parameters: a reference to a function that will be called when a matching file is found, and a list of directories to be searched. And it should Just Work(tm).