My iPhone 6 keeps restarting. How can I fix it?

So today I was on my iPhone and I put it in my pocket after checking my email. I take it out 30 minutes later and my phone kept restarting over and over, and I fiddled with the power and home button and got it on. I do some web surfing on it, put it away and I take it out later. Lo and behold, it is restarting in a loop again. I was annoyed, and I put it away and now I can't even get into the phone. Is there something I can do besides a compete restore to fix it?

Will I be charged for long-distance texts?

I have this friend who is abroad for a little while. She does not have an iPhone, so i can't use iMessage. And I'm not sure if she even has access to internet.

Will I be charged if I text her via SMS? If so how much?

Also, I do not have an international phone plan.

What is the best video editing software?

I'm looking for a video editing software for Windows, or an app for iOS where i can change the color of just one thing in the video instead of adding an overlaying filter to the entire video, For example I'm trying to change the skin color of my friends and I to green just as a fun little project, but only the skin color! I'm willing to spend some money on this, but I'm not Bill Gates so don't hit me with a $100 product.

If this matters,
My computer can run just about any software you throw at it, and is powered by windows 10
My phone is an Iphone 6 fully updated