The organ duo and trio are contrapuntal textures--that is, two or three individual horizontal lines that work together in “counterpoint” (melody against melody). Contrapuntal textures usually consist of 2, 3, 4, or 5 individual parts distributed between the two hands and feet.
The three-step and seven-step methods can also be applied when learning pieces of a less contrapuntal (“homophonic”) texture. Conceived of more vertically, these textures usually include one part that is more chord-like in nature--often containing three notes in one hand at a time. There is no need to break down such a part horizontally.