开火 

Pinyin: kāi huǒ  
Meaning：Fire
Sentence: 开火之前仔细瞄准目标。Take careful aim at the target before firing.

More: 

开： 

Pinyin: kāi
Meaning: Open; start
Radical: 廾
Stokes: 4
Traditional: 開
Common words/Phrase:
开始 [kāishǐ] 【begin】
开心 [kāixīn] 【to feel happy】
开发 [kāifā] 【explore】
开通 [kāitōng] 【open up】
开放 [kāifàng] 【to lift a ban】

火：

Pinyin: huǒ 
Meaning: Ammunition; anger; fire; urgent
Radical: 火 
Stokes: 4 
Traditional: 火 
Common words/Phrase:
火红 [huǒhóng] 【fiery; flaming】 
火速 [huǒsù] 【urgent; pressing】 
发火 [fāhuǒ] 【get angry; lose one's temper】 
引火 [yǐnhuǒ] 【kindle a fire】 
火锅 [huǒguō] 【hot pot】