Re: really easy i just need to know how
I presume you found it above the pinion facing forward.
These have a tendency to rust as they are just Iron on iron. Really, it's just a 3/8 drive square, I usually just use an extension and ratchet. Spray the crap out of this thing with some rust penetrant like a day before, this will make life easier. The key is to try to find an extension with no lock ball on it so that it will be a snug fit. If you think you will mutilate the plug getting it out, buy a new one before starting.
The brute force method involves using the same tools mentioned above, only this time you hammer the extension into the plug, only offset by 45 degrees so that it bites into the plug. This will mutlilate it for sure, but it will help get it out.
If ALL else fails, drop 10$ on a screw extractor (reverse threaded), I have a kit of them for just such an occasion.