so / too / either / neither / nor

So is used to show agreement with positive statements.

So + Auxiliary/Be + Subject (pronoun)

The Auxiliary (or To Be/Have) needs to agree with the verb tense in the original statement.

It is similar to using TOO at the end of a sentence.

Example:

Person A: I am happy.

Person B: So am I.

Person A: I'm going to Brazil in the summer.

Person B: So am I.

Person A: You look nice today.

Person B: So do you.

Person A: Stephanie has a new boyfriend.

Person B: So does Mary.

Sometimes you can use So + Auxiliary + Subject as a continuation of the first part of the sentence.

Example:

John can sing well and so can his brother.