Youre going to have the WiFI sign come up by the Verizon sign, which shows youre using WiFi. Then, 3G will come up by the Verizon sign, showing you that youre using 3G.
Just go under Setting > Wifi and activate the Wifi and choose the name of your network and your iPhone will automatically connect to your Wifi connection even if it is connected to the 3G (4G) network, thus you just deactivate the cellular network if you would like to use just the Wifi