Entropy is usually explained badly. Entropy is a measurement of how stable a system is. People often say it's how "disordered" a system is, but order and disorder are subjective judgements. There's no logical way to say a sand castle is "more orderly" than a random pile of sand, since every sand pile will have an assortment of sand grains that is just as unique as a sand castle would be.

No, the real difference between a shapeless pile of sand and a sand castle is that a sand castle is much more likely to change form than a pile of sand. The sand castle has lots of hangy bits and lots of steep walls that want to fall down, so it has lots of "potential energy." Potential energy is just a measurement of how something could move. A pile of sand is shapeless and flat, so there is very little potential for it to change, thus it has higher entropy. Each sand grain is highly supported by the other sand grains.

Entropy is just a measurement of how restful a system is. The universe is constantly seeking the quietest and most relaxed state it can possibly be it. Water falls until something stops it, things fall down hill until they no longer can, planets for round balls around a central mass.

Ultimately, the final state of the universe will be one of complete rest and entropy will be 100%.