Once you install 3G Unrestrictor, you will have the app icon on your home screen. To use it, just start the config app and press the edit button, followed by the + button. Any app you add in the following screen will be able to use the internet on 3G without any restrictions.
Note: You can add any app you want, but only apps that are somehow restricted on 3G, will behave differently.
Adding mail to the list for example, will not do anything, since it has the same capabilities on 3G and WiFi.
But adding the Twitter app "Tweetbot", will allow you to live stream tweets on 3G or LTE, which usually only works on WiFi!