1) The molecule "3-ethoxy-4-benzaldehyde" doesn't really make sense. The aldehydic functionality is assumed to be in the "1" position, and with the "3" position occupied with the ethoxy group, the "4" doesn't describe anything. So I'd say it's the 4-hydroxy.
2) So, you're reducing something in this experiment. Think about what functionalities you have in your molecule. Will you reduce the hydroxyl? Ethoxy group? Aromatic ring? Aldehyde? What can be feasibly reduced? Check out
http://en.wikipedia.org/wiki/Sodium_borohydride#Organic_synthetic_applications and that'll show you sodium borohydride's application.
3) What is sodium borohydride? The most important part, the boro
hydride is a source of hydride ions (H
-). Are nucleophiles electron-rich or electron poor? Go from there.
Good luck!