Grammar: Building Simple Sentences (语法 - yǔfǎ)
Basic Sentence Order
Use 
是 () to say what someone or something is.
Pattern: Subject + 是 (shì) + Object
我 是 老师。
I am a teacher.
他 是 学生。
He is a student.
她 是 中国人。
She is a Chinese person.
Use 很 (hěn) to describe people or things.
Pattern: Subject + 很 (hěn) + Adjective
我 很 好。
I am fine / I am good.
老师 很 好。
The teacher is good/well.
Think of 很 (hěn) here as a necessary connector that links the subject to the adjective. No verb is necessary.
Asking Yes/No Questions with 吗 (ma)
The simplest way to turn a statement into a yes/no question is to add the particle 吗 () at the very end. The word order of the statement stays exactly the same!
你 是 老师。
You are a teacher.
你 是 老师 吗？
Are you a teacher?
他 是 美国人。
He is American.
他 是 美国人 吗？
Is he American?
Negation with 不 (bù)
To make a sentence negative (to say "not"), place 不 () directly before the verb:
我 不 是 老师。
I am not a teacher.
Bù becomes bú before a 4th tone like shì due to tone sandhi, a tonal adjustment rule. This is basically to make the pronunciation more fluent.
她 不 是 学生。
She is not a student.