The String theory is a complicated one. It basically states that every particle in the universe is actually a string. As the string vibrates quickly, an image of a particle is produced. This theory could show the connection between particle-wave duality, in which particles are waves and vice versa.
This is an example of the string theory: when two balls collide with each other at different angles, they are deflected into opposite directions. When a particle and anti-particle collide with each other at different angles, they create a brief explosion that creates light. The photon in the wavelength of light releases its energy, creating another particle/anti-particle pair. These two begin to travel in separate directions as if they were the two balls hitting each other. If one connects the history of all of these events, one may see that 'two lines' merge into one and then back into 'two lines' again. Particles may be thought of as one-dimensional strings. The particle and it's antiparticle may be thought of as the vibrations on these strings, or in other words, the points where 'two lines' exist. So basically, the string theory explains that objects are not particles, but strings. When these strings diverge, two opposite particles exist.