Measure words: 个 is not enough
In Chinese you can't put a number directly before a noun. You need a measure word in between: 三本书 sān běn shū, "three [volumes of] books".
个 gè works as a general fallback, and native speakers understand it, but it sounds childish if you use it for everything. The five I reach for most:
| Measure word | Used for | Example |
|---|---|---|
| 个 | people, general | 一个朋友 |
| 本 | books, notebooks | 两本书 |
| 张 | flat things: paper, tables, tickets | 一张票 |
| 杯 | cups, glasses | 一杯茶 |
| 只 | many animals | 一只猫 |
Note that with two you say 两 liǎng, not 二 èr: 两本书, never 二本书.
grammar