Does downloading apps on Wi-Fi use data?

Iphone 5 AT&T

Any time you are downloading or uploading, your are using bandwidth/data.

Yes of course you're using data, but whose data are you using? You're own internet connection? Or the Wi-Fi from a free public source that is the question? If you want to save money on data usage go to a free Wi-Fi source and download your apps from there.

I don't have data service.
on my blackberry I had to set phone all up for data service, and set up my Wi-Fi for my home router. But using browser doesn't use the data service, it uses my Wi-Fi.

try using the browser a little some on your home router, then check your bill at end of month, to see how much of the data plan was used. If you don't have a data plan, ask AT&T how much it costs to use data if you don't have a data plan.

avoid videos and sites with large amounts of images "pretty graphics". Those are high-bandwidth.
a page designed with photoshop may look great, but it's awful for mobile.