No matter is a conjunction. It can be used with interrogative words like who, whose, what, which, where, when and how.
I will follow you no matter where you go.
Note that after no matter we use a present tense to refer to the future.
I will love her no matter what she does. (NOT I will love her no matter what she will do.)
No matter and its clause can come before or after the main clause.
No matter what she does, I will love her. (Note the use of the comma)
You will be welcome no matter when you come.
No matter when you come, you will be welcome.
The expression ‘no matter what’ means whatever. In the same way, the expression ‘no matter who’ means ‘whoever’.
No matter what she says, I won’t trust her again. = Whatever she says, I won’t trust her again.
Clauses with whatever, whoever etc., can be used as the subjects or objects of their clauses.
I will believe whatever she says. (Here the clause ‘whatever she says’ is the object of the verb believe.)
Clauses with no matter what / who / when etc., cannot be used as the subjects or objects of their clauses.
I won’t believe her no matter what she says. OR I won’t believe her whatever she says.
But we can’t say ‘I won’t believe no matter what she says’ because clauses with ‘no matter what’ can’t be objects.