I want to learn exact use of english grammar. Please brief me about tense.
Welcome to the forum.
We are not here to take the place of your grammar books and dictionaries. We are here to answer specific questions about problems you have with the English language.
Read the other posts in the forum and you will see the types of question we deal with.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.