口 kǒu

• 开口 (kāi kǒu) Open one's mouth
• 口音 (kóu yǔ) Accent Literal. Mouth sound
• 口水 (kǒu shuǐ) Saliva Literal. Mouth water
• 口琴 (kóu qín) Harmonica Literal. Mouth string-instrument
• 口红 (kóu hóng) Lipstick Literal. Mouth rouge
• 口罩 (kóu zhào) Mask Literal. Mouth cover
• 人口 (rén kóu) Population Literal. Human mouths

• 门口 (mén kǒu) Doorway Literal. Door opening
• 入口 (rù kǒu) Entrance Literal. Enter opening
• 出口 (chū kǒu) Exit Literal. Out opening
• 路口 (lù kǒu) Road junction
• 港口 (gang kǒu) Port

For something that comes out of one's mouth or has an opening

• 一口气 (yī kǒu qì) A breath Literal. One mouth of airflow
• 说一口流利的英语 (shuō yī kǒu liú lì dè yīng yǔ) Speaks fluent English Literal. Speaks a mouth of fluent English
• 两口井 (liáng kǒu jǐng) Two wells Literal. Two openings of well

Compound characters with 口 Mouth Radical are usually part of the mouth, mouth-related activities or expressive sounds

• 舌 (shé) Tongue
• 嘴 (zuǐ) Mouth
• 唇 (chún) Lips
• 吃 (chī) Eat
• 喝 (hē) Drink
• 唱 (chàng) Sing
• 叫 (jiào) Shout
• 喊 (hǎn) Scream
• 嘿 (hēi) Hey
• 哇 (wā) Wow
• 吗? (ma) Or not? – ending particle to indicate a question
• 呢 (ne) Where? / Who? / Why? – ending particle to indicate a question

P.S. 口 Mouth Radical