Clay particles are the finest of all the soil particles. They are the Lynyrd Skynyrd of soil so to speak. Clay is nutrient rich and doesn't allow for a lot of airflow.
Silt particles are larger then clay particles but are still invisible to the naked eye. Silt is considered to be the most desirable soil as it allows air and water to flow but still provides nutrients for plants.
Sand is very loosely packed. Sand is the largest soil particle and is very common in freshwater biomes.