If I'm connected to Wi-Fi and I download a free app, will it use my data? - 1

I barely have any data left but I really want this app. If I'm connected to Wi-Fi and I download it, will it use my data? I have an iPhone 4 by the way, if that changes anything.

It will use data if you are using the phone

It will not affect your phones data. But make sure you have a good Wi-Fi signal otherwise if it drops out during the download it will then start using your phones data storage.