star-wars-the-old-republic
On Tython I found a datacron containing a Blue Matrix Shard. I was told that I could combine them in some sort of combiner on Coruscant. Which leads to a couple important questions:
(I think this info is best in one question/answer, but let me know if it should be split.)
If you want to make sure you got all the datacrons on a specific planet, look at the Codex entry for that planet and then click on the magnifying glass. It shows your progress on that planet, including how many of the datacrons you have:
As for the rewards from datacrons, it seems it's only stats boosts and matrix shards, but I can't say that for certain.
You cannot change factions in TOR — what you pick is what you get.
That said, there are small differences depending on whether you are Light Side / Dark Side, such as verbal cosmetic changes in conversation. And your choices may affect companion affection.
Flashpoints are repeatable and have up to +/- 250 points' worth of dark/light decisions among them, and Diplomacy crew missions can yield DSP/LSP as well, so you can always completely reverse your stance (although that could potentially take a /lot/ of work...).
Best Answer
Three shards can be combined using an Assembler to form a Matrix Cube; the cubes are then used in your character's Relics slots. There found on all the planets and only in datacrons.
As far as the number, there are 67 datacrons. However, there are a limited number of shards to be found (3 red, 3 yellow, 3 blue, 2 green--98% sure, again).
Here's a video walkthrough with more details on how to use them:
This is the most comprehensive guide I could find on the locations of the datacrons (including those with shards):
http://www.republictrooper.com/datacron-locations/