So, when you combine the two ideas, the fields, which before were thought of as continuous, are no longer continuous, but made up of quanta, or particles. The quanta that 'mediate' the electromagnetic field are called photons. The quanta that mediate the gravitational field are called gravitons. So, after the advent of quantum mechanics, the language changed from fields conveying information to particles conveying information. The basic idea is the same, a particle interacts with other particles due to a field.
Nobody knows the answer.
One way to think of the Planck length is that it is the scale at which nobody has the foggiest idea what happens. Not yet, anyway. String theory is an attempt to understand Planck scale physics, but it has a long way to go before it can answer these kind of fundamental questions. There are some people who think the universe popped into existence as a sphere with the diameter of the Planck length. Or, at least, they think that this is a good approximation to what might have happened and they can calculate various properties of such a universe.