Sideways Video and Editing Software iPhone

Okay, so I was at a concert. I held my phone in portrait mode, it videoed in landscape so it is 90 degrees rotated. When I rotate my phone it rotates and I cant see it correctly. What did I do wrong? How can I avoid this in the future? What made it do that?
Now, how can I edit on my phone before I upload to you tube? Is there free/cheap software or do I have to do so on my PC and if so, what cheap software?
Windows XP