BibTeX, biblatex and biber ⇒ BiBTeX \& TeXShop

[maxbauper]

I'm new here, and I am looking for some help.
So, I am using texshop to write my document and bibdesk for my library, and I want to use APA style in my bibliography. I've dowloaded the apacite package, and in my document: I've done: \usepackage[apaciteclassic]{apacite}, \bibliographystyle{apacite}, \bibliography{<filename>}. But when I do \cite{<example>} to cite a reference in my bibdesk bibliography (in a .bib file), it doesn't appear in the text. When I compile (?,?) this appears and says that "LaTeX Warning: Citation `xxx' undefined on input line xx.
I am missing something? What can I do?
Help much appreciate it