Here's how I use the external render.

1.  Make sure you have selected exactly how you want your scene to render (size and all the other setting).  

2.  On the render setting screen select External Render, select edit.  Select either Local Standalone render or network.  This will select the Render to Disk option.  Make sure the file name and path is what you want.  Click OK to close the render setting dialog.

3.  Save your Vue file and close it.

4.  Open a new blank scene.

5.  Click Render, Batch Rendering.  Sometimes the render will already have the file name there if you were rendering it and aborted.  Click Clean Finished to remove any files and then click the Add button to locate the Vue file to be rendered.  

6.  Wait for the render to finish.  You should see a DOS looking window with the status of the render showing what percentage is done.  You can minimize or close them.  For best results and time savings, don't use the computer for other stuff. 

LVS - Where Learning is Fun!  
http://www.lvsonline.com/index.html