I don't know if I'm smart or not, but I do know a little something about what you're asking =)
And I'm telling you, get those books and do a little self research, b/c the answers you're looking for are not found in a paragraph on an internet forum.
Why don't you ask a very specific question, b/c frankly its akin to asking someone 'what's the history of Europe like, someone has got to know a little something?'
But here's a paragraph all the same.
General relativity is Einstein's theory of gravitation. It involves the geometrization of space and time and making that the primary source term for generating gravity, its a very large scale force. Quantum mechanics + special relativity, is the study of the very small (the remaining 3 forces in nature). Both theories are well tested experimentally in their own domains of validity. Mathematically however, they don't mix well. In part b/c GR involves compact, more or less continuous geometry, and quantum mechanics discrete 'fuzziness' and potentially nonlocal effects. When you mix them in a naive quantum version of gravity, you get a theory that involves gravitons that output pathological infinities (read nonsense). In a sense, the theory breaks down. So we expect something 'new' to emerge, in much the same way that Fermi theory of weak decay broke down and led to modern Electroweak theory.
String theory is one attempt to get past the problem, essentialy removing the point particle as a fundamental unit, and instead postulating a 1dimensional or larger 'brane' to replace it. Geometry in string theory, then is an emergent 'field' just like all others, and not truly fundamental. Particles and forces are interpreted as excitations of various 'string' modes of oscillation.
Please understand, that at the level I am talking at, these things are very unprecise and in many ways WRONG. But that's the way things are, in a field that as yet is still work in progress.
