Each kanji has multiple readings–音読み, the Chinese reading., and 訓読み, the Japanese reading. The author of the hilarious manga 『日本人が知らない日本語』 (The Japanese That Japanese People Don’t Know) goes into the reasons for this–namely that when the Chinese brought over kanji, the Japanese already had their own words for things like mountain, river, and person, so they took both their own word for what the kanji represented AND the Chinese pronunciation. Hence, the character 山 was read san in Chinese and yama in Japanese, and the character means mountain.
Take 読 (to read). In Japanese, the 訓読み is usually used when the character is on its own (読む, yomu, to read); the 音読み is used when the kanji is in combination with another kanji (読書, dokusho, reading)–and sometimes not, like 読み物, yomimono, reading material.
Now, ordinarily I find kanji readings to be somewhere on the outer circles of hell, as my ability to recognize more characters than I can pronounce occasionally makes me look illiterate. Sometimes, it’s fun, though.
Today’s kanji is 風車. This one is great because it can be pronounced two different ways, AND the meaning changes based on the reading.
The kanji 風 is read フウ (fuu) or フ (fu) for the 音読み and かざ (kaza) or かぜ (kaze) for the 訓読み; it means wind; air; style; manner. The kanji 車 is readシャ (sha) as the 音読み and くるま (kuruma) as the 訓読み; it means car.
Put them together, and you have
風車 (ふうしゃ, fuusha): windmill
風車 （かざぐるま, kazaguruma): pinwheel
Pretty cool, huh?