How do you get the corners all nice?? Any good tips!???

Thanks!!!

Start with the corners first. That way, you won't end up with as much excess fondant at the corners. I've just found it much easier this way.

Once you've covered a square cake, you can cover anything!

Im in agreement with chocolateandpeanutbutter. I first put on the fondant and smooth the edges on top then work the corners with powdered sugar hands (take off the rings made that oops a time or two). Good luck.

Now, do you have to cut at all and smooth back together, or do you do it in just one big sheet like the rounds?

You put it on one big sheet. Just like pp's said. Smooth the top, then the corners.

HTH!