the main idea in relativity theory is that you cannot determine the value of the variables in your equation without determining the "environmental conditions" first. Einstein called this "inertial reference frames".
an atom of plutonium is physically different in free space, than at the center of the sun. the two locations are seperate reference frames.
once you determine the factors that define a reference frame, i.e., - velocity, density, temperature, the forces that bind together the other objects near you, the rate your clock is counting the passage of time, etc. then you can determine the actual values for your subject. i.e. its length, width, height, and in the case of plutonium the rate of radioactive decay. (time realization).
Einstein's most profound discovery was that time was a variable in a mathematical equation.
always before him time had been assumed to be a constant.
now, we say, "the speed of light in an absolute vaccuum" is our best natural constant. a point of reference that doesn't change.
without a good, unchanging constant, all mathematical analysis would be impossible. only approximations at best.
But the realized speed of light in any reference frame is variable.
when a light wave is produce in the sun, it is moving thru a plasma state collection of matter. plasma is very hot very dense, and is a zone of high quantum field densities.
a quantized system is one in which the values of measured variables can only be "integer" numbers, 1,2,3,4, etc.
if you measure the energy of a proton it can only be, say 1 electron volt, (the unit of measure is for electrons but measure electric field energy.) if i want to accelerate, (increase the energy of) the proton, i have to give it a whole quantity of energy, 1 more electron volt, to arrive at 2 ev in one jump.
That's why they say, "make a quantum leap". electrons around a nuecleus do that. and when the electron falls back to its original energy state, it will often emit a photon, a unit of energy equal to the quanta of that system. this determines the color of the photon.
to think in relative terms, will cause you to have an uneasy state of mind at first. most of us think in "newtonian" ways.
i.e., there is a "recipe" or one set of instructions, that if followed will yield an expected result.
but in relativty, basic rules stay the same, (laws of physics), but all the numbers change as the "reference frame" changes.
if i try to detonate a nuclear bomb, the act of setting off the conventional explosive to compress the plutonium, causes the measurements of the plutonium to change, therefor i have to use the amount of explosives based on what the measurements of the plutonium WILL BE, when the explosives produce new conditions for the plutonium.
thats as close as i can get to explaining relativity to a non scientist.
hope it helps