It is an ancient principle in the understood laws of physics that mass and energy are essentially different aspects of the same thing.

Mass, any mass, is nothing more than a bundle of energy tied up in a certain way. It is, however, which of many "certain ways" the energy is tied up that defines it's properties.

One convenient way to look at it is on the atomic and sub-atomic level. Protons, electrons, and neutrons (the most commonly known sub-atomic particles; for purposes of clarity, we will skip discussion of some of the more exotic members of the sub-atomic family, like neutrinos, mesons, tachyons, tau-hadrons, psi-leptons, "gypsies", quarks, gluons...) can all be considered small bundles of energy. Protons carry predominately one form of energy, which we conveniently call "positive"; electrons carry another form of energy, which we conveniently call "negative"; neutrons really have a third form of energy, which we sometimes conveniently call "neutral" but may actually be just a combination of the other two forms. Nature, you see, likes to keep the books balanced.

Stable masses tend to occur when large numbers of "positive" and "negative" particles (i.e., protons and electrons) join together, often with the aid of "neutral" particles (i.e., neutrons) to keep the peace. Particles of like energy tend not to want to stay near each other, you see, while particles of opposite energies tend to want to stay together. When protons, electrons, and neutrons join together in a stable form, it is called an "atom". Much, perhaps most, of the universe is made up of atoms.

Not surprisingly, the most simple arrangement of this kind (one proton and one electron) is also the most common.  It is often joked in certain scientific circles (when they are not, for instance, telling uproariously funny one-liners at each other concerning quantum mechanics, unified field theory, or the amazing things one can do when they reverse the polarity of the neutron flow -- do not ask us to explain the latter) that the entire universe consists of two things -- hydrogen (our one proton and one electron arrangement) and debris (everything else).

Accordingly, being the most common, basic arrangement, hydrogen is also the primary building block for everything else, the so-called debris. Why "debris"? Because when you start putting atoms of hydrogen together, they begin to interact. The more hydrogen you put together, the greater the interaction. Individual atoms also have an attraction to each other, which we often call "gravity" (actually, both the "strong" and "weak" nuclear forces figure rather prominently into this, but since we're not opening our discussion to tau-hadrons or reversing the "polarity" of supposedly neutrally-charged particles like neutrons, there is no reason to include either of these into our discussion), and when you get enough atoms of hydrogen together, their gravities combine and they start to get really close to one another. The more hydrogen, the closer they get. Add a considerably LARGE amount of hydrogen, their combined gravity becomes so huge that the atoms are packed in with virtually no space between them. Add even more hydrogen, and the pressure builds to the point that something has to give. Almost always, something does.

Perhaps it is an errant tau-hadron crashing the party, or maybe it's just because packed in like that tempers will always flare. Whatever. The point is that, packed in that close, the moment one atom is hit by another (or, more usually, when one atom is hit by a particularly malicious neutron) with enough force to shatter the positive-negative bond, it causes that victim-atom's constituent particles to shoot off in turn with enough force to shatter other positive-negative bonds. And at that range (i.e., none), they can't miss. In turn, those released particles will crash into other atoms, which will cause them to fly apart and crash into other atoms, which will... well, you get the idea. The result is quite spectacular.

Energy. Or, to be more precise, a thermonuclear chain reaction.

The debris from this will eventually combine into more complex forms, because in order to break such a simply effective construction as one proton and one electron and go to, say, a construction with two protons and two electrons ("helium"), you need energy. In other words, you need to tap the energy that keeps atoms together in order to force that energy to build something more interesting than simple, boring, hydrogen.

Now, for any intelligent species that aspires to something more than roots, berries, and trying not to be eaten, there will eventually come a time in it's development when someone figures all of this out. Quite a number of them also realize that you can do the same thing far more compactly with certain other materials (like uranium or plutonium), and get essentially the same result. Every once in awhile you also find a species who gets a tad carried away with this thought, especially in some of it's more strategically applied aspects; for them we have the universal accolade "morons".

Thankfully, most species aren't morons.

The point is, the realization that one can create energy from mass leads inevitably to the theoretical possibility that one can also create mass from energy. Thermonuclear energy, after all, proves that mass is nothing more than energy organized, and energy is nothing more than mass disorganized.  Armed with this knowledge, and keeping in mind several other miscellaneous bits of trivia (the speed of light, the ratio of the circumference of a circle to it's diameter, the fact that neutrons really do have polarity if you break them down into their constituent quarks), it is possible to deduce a hell of a lot about the rest of the universe. And most importantly, how one can make a lot of money with this knowledge.

But to combine order and disorder is never easy; just ask anyone who's had to slug a few rounds with a textbook on chaos theory, and you'll get the picture. Yet, it has been done, and quite profitably too.

It is called the matter transmitter.

The theory is simple. So simple in fact that, on Earth, it took an army of patent lawyers and an eternity of litigation to sort out. Take an object, any object. Say, a flower pot. Put said flower pot into said matter transmitter.  Turn said matter transmitter on. Said matter transmitter will proceed to record the distinct, unique energy pattern of said flower pot. Then, it will break said flower pot into it's basic energy form, transmit both energy and pattern to another matter transmitter, which will in turn take the energy and re-assemble said flower pot. Then, presto! You now have a flower pot sitting beside your matter transmitter on Beta Epsilon III, where it will be revered as a sacred icon for centuries to come.

This is, of course, only a rough explanation for something far more complex. If you want a more detailed discussion, we suggest looking up that Scottish engineer we hear so much about. This explanation does not, for instance, take into account the decades of research and billions in cost-overruns needed to produce a transmitter capable of receiving something more than a human-shaped vegetable, nor does it take into account the frenzied activity in the transportation sector when news of this development hit the stock exchanges.