I'm going to assume you know about the whole Cosmere thing. Shards are basically the gods/magic batteries of the planets or in the case of the splintered ones,just batteries. They create things,destroy things,and just do whatever gods do. Except they're not really gods,more like 1/16th of a god called Adonalsium but if you divide infinite power by any number,you still get infinity,sooo they're god-like? I dunno.
As for the names,each Shard is bound to a certain Intent,as it were,meaning Preservation has to preserve and Ruin has to...well ruin. As for the Splintered ones there's one Shard called Odium(actually Hate/Passion) who's the big bad and wants to rule the Cosmere so he went about and wrecked,like what? 4 Shards? This kills the people wielding the Shards and makes it kinda difficult to pick them up again.
Hope this clears things up.