头 — how to use it in Chinese

As tóu it means head or end of something. Functions as a measure word for large animals: 一头牛 (one cow). Also forms compounds like 头疼 (headache).

As a suffix, tou loses its tone (neutral syllable) and attaches to position words: 里头 (inside), 外头 (outside), 上头 (above), 下头 (below).