Here is an old tech talk video. (101 MB)http://www.hash.com/ftp/pub/movies/NetRender.mov
The original netrender connected several network connected computers together to make a render farm, so you could have many computers rendering an animation.
The netrender that comes with v16 allows you to render on two cores of your cpu at the same time. (Or on another computer if you have another computer connected to your home or office network). This will speed up rendering of your animations 2X, since there are two cores (or processors) rendering at the same time. But it will not speed up rendering a single image. A single image only renders on a single core (or cpu).
The main usefulness (in my opinion) of the netrender that comes with v16 is that you can set up several "jobs" (choreographies) to render overnight and netrender will automatically start rendering the next job when the current one has finished. Before v16, you had to wait until one project rendered, then manually load the next project, render it, wait for it to finish, then manually load the next project etc etc.