What exactly is fate? Can you change fate or is it already determined?

Fate is generally the idea that each and every person has a specific path to follow. As we make choices in our lives our fate could change. We could have two different options ahead of us and depending on the choices we make in life we could end up on either road.
It's hard to say if fate is pre-determined or if it can change along the way. This subject is very debatable. I suppose if really depends on what you were taught, what you believe, and the decisions you make in life.

Hope that helped.

As far as I know, fate and destiny are pretty much interchangeable. Fate is the outcome of your life's path. It is what was destined to happen to you. You can make different choices, but whatever you end up choosing is what you were fated to choose and so your end result will always be the same. Kind of like those "choose your own adventure" books where you can never get away from the creature in the cavern, no matter what path you take.
If you believe in fate and destiny, you must accept that you cannot change it. Fate is fate is fate and that is the end of it. You can't change your fate.

I don't buy into the whole idea of fate and destiny, personally. In my opinion, the future is not set. There is no fate but what we make for ourselves.