The Kodály approach emphasizes the importance of learning how to sing on pitch. In the 18th century, John Spencer Curwen drew upon an earlier music teaching system known as Norwich Sol-fa, which had been devised by Sarah Glover, and developed hand signs to go with the solfege syllables (do re mi, etc.). Kodály integrated these hand signs into his teaching methods.
Hand signs are a way of giving a physical placement for a vocal pitch. The low "do" begins at your midsection. Each pitch is then above the previous one. Thus, you have the hand signs going up when the pitch goes up. The upper "do" is at eye level.