五 was once an X drawn between two lines — heaven above, earth below, and the five elements crossing and interacting in between. The X is still there in the middle of the modern character, where yin and yang meet.
Five organizes the Chinese universe: 五行 (the Five Elements — wood 木, fire 火, earth 土, metal 金, water 水, several of which you now know), 五味 (five flavors), 五官 (five facial features). The number structures traditional medicine, cooking, and philosophy alike.
An X (yin and yang crossing) caught between two lines — FIVE.
五行 (the Five Elements) include 木 (wood), 火 (fire), and 水 (water) — three characters you've already learned. Chinese thought builds the whole cosmos from five.