I have a iphone 6 if i'm on Wi-Fi i'm using a data?

I have a iphone 6 if i'm on Wi-Fi i'm using a data? - 1

No. You're not using your cellular data. You're using your ISP data which is different.

The answer really depends on where does your Wi-Fi comes from.

Data is not used when on Wi-Fi

No. Wi-Fi is prioritized over data.

On Wi-Fi, you are not "charged" for the data

No you're not. You're using your home Wi-Fi, which means that you don't use your cellular data at all, unless you turn of the Wi-Fi feature of your phone.

No… Your smart device detects Wi-Fi and connects automatically when in range so your mobile data(3G,4G) is only used when your not in range of Wi-Fi