What he said. Don't worry, it's idiot proof.
The .44 special is the weaker of the two rounds, and is shorter. The .44 mag is the stronger and is longer.
A .44 magnum can shoot both: its cylinder is long enough to support the magnum round and the gun itself is designed to handle the stresses of the more powerful magnum cartridge.
A .44 special is NOT able to handle the stresses of a .44 magnum round, but thats okay since its cylinder is too short to accept the longer magnum round (at least while still allowing the cylinder to rotate, which is necessary for the gun to function). Naturally this is by design.
No, I don't have much experience with either round nor do I own a gun chambered in either, so feel free to correct anything I've said here in error...but as far as I know thats the way it works (as Telcote said, same as .38spl/.357mag)
Mike
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"A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." -Robert Heinlein