How are the eight trigrams different from the 64 hexagrams?
Each of the eight trigrams has three lines and represents a basic pattern associated with Heaven, Earth, Thunder, Wind, Water, Fire, Mountain, or Lake. A hexagram stacks two trigrams into six lines, showing how two forces meet, support, or restrain one another.
The trigrams are like basic vocabulary; the 64 hexagrams are complete sentences. Read the upper trigram as one side of the situation, the lower as another, and examine whether their relationship is coherent rather than memorizing only a title.