不 / 没(有)
Two negators: 不 negates will, habit or quality; 没 negates past events and 有
HSK 1HSK 3.0 · 1
不 + V/Adj (present, future, habit, wish) | 没(有) + V (action that did not happen / has not happened yet)
不 is used for present, future, habits, wishes and adjectives: 我不喝酒, 明天我不去, 这个菜不辣. 没(有) negates an action that did not or has not happened: 昨天我没去. The verb 有 is negated only with 没 (never 不有), and 是 only with 不 (never 没是). When negating a sentence with 了, drop 了: 我吃了 → 我没吃 (not 没吃了). Ask yourself whether you are talking about will/habit/quality (不) or about whether something happened (没).
Tested at every level; HSK 1–2 true/false listening items often hinge on 不 vs 没.
Examples
我不喝咖啡。
I don't drink coffee.
昨天我没去学校。
I didn't go to school yesterday.
他没有哥哥。
He doesn't have an older brother.
我今天不想出去。
I don't want to go out today.
这个菜不辣。
This dish isn't spicy.
Exercises
1.我 有中文书。
2.昨天我 去公园，我在家看书了。
3.他 是老师，他是医生。
4.我明天 去上班，我休息。