String Theory

"When we say strings are tiny, we generally mean strings that haven't had a huge amount of energy pumped into them. But the more energy you pump into a string, the more widely it will vibrate and, at some point, the longer it will grow. So it's really a question of how much energy the string embodies. Typically they don't embody that much, and therefore typically they are very small."

Right, my question basically is the following:
What is force?
What is energy? (as explained in String Theory, physicists that don't like the String theory and think I should have posted this on the philosophy&debate forum, buzz off for a minute, I want an answer )

As I understood it thus far, string form both mass AND energy. But on the second thought, that has to be wrong(given the above excerpt of an interview with Brian Greene). So the word I was looking for must have been force (carriers) (the 4 discovered or maybe more, some which we can't observe, ever) instead of the word energy.

I've kept my question very simple, I hope the answer will be equally simplistic

But perhaps that's just as optimistic as hoping humans will be able to understand the universe, fully.