For the layman that doesn't really know what a primary entry point entails, it essentially allows you to do the equivalent of rooting/jailbreaking/homebrewing on your 3DS. This new exploit uses the game SmileBasic which is available on the Nintendo E-Shop for $9.99. If you want it, you had better do it quickly, because Nintendo will likely take the game down quickly after the exploit is released.
The exploit and tutorial is available here.