If you would like to say to be in Mandarin you use shì是. Differently than in english, shì是 doesn’t change depending on person or time but always stays the same.
As described in the blog about Adjectives, you don’t use to be to describe Adjectives in Mandarin but you would use hěn 很 instead.
If you want to describe however where you are from, who you are or what profession you are you would use shì是.
If you would like to make a sentence negative, you would use bù 不. bù 不 always stands infront of the verb.
Here are some example sentences:
She is American tā shì měi guó rén 她是美国人
He is not English tā bù shì yīng guó rén 他不是因果人
I am John wŏ shì John 我是John
You are a teacher nĭ shì lăoshī 你是老师