Lightsabers are the iconic weapons of the Jedi (and the Sith). They are very rarely seen in the hands of anyone else. Both Jedi and Sith frown upon their use by others, which is a surprisingly effective deterrent for most. Lightsabers are also very impractical weapons. They not particularly difficult to use as such; ignite the blade and then hack away at your enemies. Just be sure you are very, very careful, for even the smallest mishap could have you maiming or killing yourself. And since your enemies are likely to be carrying blasters...you'll be dead long before you can bring your blade to bear. So better leave lightsabers to the Jedi - they train with them daily from childhood...and they have the Force as their ally. And said Force grants them superhuman reflexes, phenomenal peed, and the ability to deflect blaster bolts. So in the hands of a common soldier lightsabers are largely worthless, but in the hands of a Jedi they are absolutely lethal.

A lightsaber blade consists of hyper-energetic plasma, contained within a stable looping containment field. The field keeps the destructive energies of the blade focused and contained, while having the secondary ability to keep other energy out - handy for blocking other lightsabers and deflecting blaster bolts for example. Contrary to popular belief an ignited blade is not 'weightless'; the plasma medium is dense enough to have significant gravitational mass. Moreover the complex interaction between the energetic medium and the containment field generates considerable additional felt inertial mass when swung. A lightsaber blade is still far lighter than a comparable physical blade, making it a much more agile weapon, but the energy blade has sufficient inertia to cut through matter, block other blades, and deflect blaster bolts.

The blade radiates very little heat and expends negligible energy until it comes into contact with solid matter or another energy field. If used actively, especially if cutting through lots of dense matter, the power consumption is somewhat higher and the Jedi needs to recharge his blade more frequently (how often is also dependent of the capacity of the lightsaber's power cell). The power of the blade is so great that it can cut through almost anything, although the speed through which it cuts depends on the density of the subject. When cutting through dense material, the interaction between the blade and matter causes some resistance; almost giving the blade a feeling of being solid. One important note about lightsaber wounds is that they rarely bled profusely, even when a limb had been severed. This is because the energy blade cauterizes the wound as it passes, and thus even a severe wound does not tend to bleed heavily.

Lightsabers cannot cut through other lightsabers (although sometimes the containment fields of two blades can fuse, causing the blades to lock up). The blades can also be deflected by other powerful containment fields. Personal deflector shields are less effective against lightsaber than blasters; a Jedi can usually force his blade trough such shields by applying extra pressure, whereas a blaster would have to be set on a very high setting indeed for it to penetrate. If face with a stronger shield a Jedi can switch of the blade, physically move the emitter inside the shield's perimeter, and then re-ignite. A dangerous move to be sure, but very effective against heavily shielded targets such as destroyer droids or tanks.

Lightsabers can also effectively deflect blaster bolts. The blade itself is about half an inch in diameter while the containment field is around two inches wide at the base (tapering to about one inch at the point). It goes without saying that only a Jedi has the reflexes, training and Force-sensitivity required to not only predict where a shot will land, but actually move his blade to intercept. Anyone else managing to deflect a blaster bolt is fantastically lucky - and either really desperate or terminally stupid. The lightsaber can also parry physical projectiles; they are not deflected, but annihilated by the blade, so reflecting bullets back at a shooter isn't possible (by a Jedi could very easily shield himself with a telekinetic shield if old-fashioned firearms are employed against him).

Various attempts - most of them failures - have been made throughout galactic history to develop lightsaber-resistant materials. Hyper-dense matter, personal shielding, Sith alchemy, and advanced materials technology have been employed in various forms. Sometimes with  some effect, but always plagued by lack of availability, cost, complexity and/or bulk. A lightsaber is a very simple and effective weapon, and if you're a Jedi you can build them from scratch at low cost if need be. So anything that's too expensive or too complex simply won't work, especially on a larger scale. Lightsabers have also been refined over the millennia to compensate for any advances in defensive measures. The best example of this evolution can be found by studying the aftermath of the Great Sith War, 4.000 years ago; the cortosis-weave used in the weapons and armor deployed by the Mandalorian Neo-Crusaders were resistant to the lightsabers used in that age. Its exact nature is still a closely guarded secret, but it is likely it was a combination of exotic materials and experimental manufacturing techniques. The point is, however, that by the end of the Mandalorian wars lightsabers have been modified to deal with this new complication, regularly defeating cortosis-weave. And a modern-day lightsaber would likely cut right through such vintage equipment, should anyone try to field it against the Order.

The only effective method currently in use is the use of force weapons; force pikes, force staffs and force blades all project sufficiently powerful energy fields that they will block and be blocked by lightsabers - mostly without damage to the force weapon. Using force weapons in this manner requires great skill and great courage. as entering into melee with a Jedi or Sith is inherently extremely dangerous!

Lightsabers are usually pretty similar; a straight hilt suitable for both one-handed and two-handed grips and a blade length of about a meter. Variations do exit; longer and shorter blades, variable length blades, double lightsabers, lightsaber polearms, etc. The difference is largely cosmetic or charters to some specific style of lightsaber fighting. There are also some variant weapons that have some characteristics in common with lightsabers; energy whips for example, while not as destructive as true lightsabers they have a long reach and can effectively fight other energy-blades. Color difference is also largely cosmetic and mostly a product of the focusing crystal matrix used construct the saber. Most Jedi Order sabers are blue, with green blades also common, yellow less so, purple sabers quite rare, and other color variations almost never seen. During the days of the old Republic domestically produced Sith sabers were usually red, but this was probably more tradition than anything else.

In conclusion; the lightsaber is as much a badge of office as it is a weapon. It is rarely drawn, but when a Jedi ignites his blade he is armed with a blade that can cut through (almost) anything and even be used to deflect enemy weapons fire.