How to make sure i'm using my home internet Wi-Fi and not my mobile data plan usage?

I've just gotten adsl with a Wi-Fi modem and i have gone into my Wi-Fi settings on my iphone 4 and connected to my Wi-Fi, there's a tick next to my Wi-Fi so i'm sure i'm connected right? But are there any other settings or anything i have to into to change so that doing things on my phone won't use the data on my phone? Or is it just a matter of connected to the Wi-Fi like i have and then none of my mobile data will be used? Need answers. I've gone over my cap by alot and need to be careful so i'm just double checking

You can check anytime by looking at the top of your screen. If you see the Wi-Fi signal next to the cellphone carrier name, your connected to Wi-Fi. If you see a 3G picture, or 4G, your using Mobile data. If you want to make totally sure you don't disconnect from Wi-Fi, you can turn your data off whenever you want. In settings, go to general, then click on cellular. You can switch cellular data off and on from there.