Learn the words first
是
shì
to be (identity)
学生
xuésheng
student
老师
lǎoshī
teacher
不
bù
not
吗
ma
yes/no question particle
Identify someone
我 是 学生: I am a student. The basic order is person + 是 + identity. Mandarin does not need an article equivalent to a here. You already met 我 and 你; reuse them with 学生 and 老师. 是 does not belong in every sentence: compare the age pattern from the previous lesson.
Negate and ask
Put 不 before 是: 我不是老师。I am not a teacher. In speech, 不 before fourth-tone 是 becomes bú: bú shì. To ask a yes/no question, add 吗 at the end: 你是学生吗？Are you a student? Answer 是 or 不是, rather than using a universal word for yes or no.
Examples to read and repeat
我是学生。
Wǒ shì xuésheng.
I am a student.
我不是老师。
Wǒ bú shì lǎoshī.
I am not a teacher.
你是学生吗？
Nǐ shì xuésheng ma?
Are you a student?