Soft corals do not create a calcium carbonate skeleton. They include corals like xenia, green star polyps, leather corals, and zoanthids, etc. LPS and SPS are hobby acronyms for two types of stony corals, large polyp stony corals, and small polyp stony corals, respectively. Stony corals generate a calcium carbonate skeleton. A polyp is basically the tentacle and mouth structure of a coral. Most corals have many polyps together in what would be considered a colony. Some stony corals have large and some have small polyps. LPS examples include brain, hammer, torch, and flowerpot corals. SPS examples include branching, encrusting, and plating varieties such as acropora, montipora, seriatopora, etc. In most simplistic terms, soft corals are easiest to keep, LPS in the middle, and SPS the most difficult. There are exceptions to this generalization. Welcome to R2R and the hobby!