This question already has an answer here:

I traveled by air from mexico with tourist visa and my passport was stamped with date of arrival. How do I know how much time i was given to stay in the U. S.?

marked as duplicate by k2moo4, Henning Makholm visas May 17 at 1:28

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.