a TOE (theory of everything) would be a theory that would explain why there is the universe there is, with the particles there are, and the forces (gravitation, strong nuclear, weak nuclear, electro-magnetic) there are. This without having to make any assumptions, or using any factors, constants, etc.
We are VERY far from that. We have a theory of gravitation on the large scale but nothing for the quantum (small) scale. We have a theory for the electro-magnetic, and for the weak nuclear forces (they are actually the same force), but it does not fit, is not integrated with that of gravitation. Ditto for the strong nuclear force. We have various tentative models (rather than theories) that try to fit the observed elementary particles - they all fail in some respects, and all of them need various constants, assumptions, etc.
And as if those incomplete were not enough, none of them includes anything about why all this is here in the first place.
String theory, or superstring theory, is an attempt to get to a TOE, starting with the assumption that, at some fundamental very very small scale, everything really would be made of very long and very thin (much smaller than, say, the size of an electron) strings in some hypothetical 11 or higher-dimensional space. They require fairly complex math. None of the string theories so far has led to any forecasts (such as "there should be a proton, it should have a mass of x, and an electrical charge of y") that could then be compared to nature.
But a theory that can never be tested cannot really be a physical theory. Because of this, many physicists outside the field look at string theory as an interesting mathematical or even philosophical exercice, but not something that has to do with physics. And many theoretical physicists who had enthusiastically embraced the field, have left it when years of work still failed to produce any measurable prediction.
This is quite in contrast with, for example, Einstein's General Relativity: it predicted that light would be affected by mass. And this was eventually measured.
hope this helps