What is 4g and how do i use it on my phone?

We'll I use to have phone that was 3g and now I upgraded to the nexus s and it has 4g and it say to turn it on. But first of all I don't really know what is 4g. All I know is that its soppuse to be faster than 3g. Is that all it does or are there any other function to it?What is 4g and how do i use it on my phone?
4G, right now, has no technical meaning, other than one higer than 3G, which basially means your providers specific wireless technology a generation above their 3rd generation technology. Of course, your provider needs to have their 4G techology deployed where you will use that phone.What is 4g and how do i use it on my phone?
4G = 4-th generation

It provides faster access to data when you navigate web sites and stream audio and video data.