个
gè
Measure word "ge"
You cannot count a noun directly in Chinese — a measure word goes between, and 个 is the general-purpose one.
Number + 个 + Noun
How it works
一个人, 三个苹果, 两个问题. The measure word is obligatory: 一人 and 三苹果 are not sentences you can say.
个 covers people and a huge range of objects, and is the safe default when you don't know the specific measure word. Specific ones exist and are worth learning (本 for books, 杯 for cups, 只 for animals), but 个 will be understood.
Once a noun is obvious from context you can drop it: 我要两个.
Examples
yí gè rén
一个人
one person
wǒ chī le liǎng gè píng guǒ
我吃了两个苹果。
I ate two apples.
zhè ge wèn tí hěn nán
这个问题很难。
This question is hard.
Common mistakes
- Counting without a measure word (三书) is the single most common beginner error.