As a student, if i want to give khums I'm not earning but my brothers look after my expenses. Also I have my savings which i don't use totally so what should I do?

You do not have to pay khoms, except for the savings which complete 1 year with you.
Example: If you received an amount on 1st of Jan 2020, you need to pay its khoms on 1st of Jan 2021.
then, If you received an amount on 1st of Feb 2020, you need to pay its khoms on 1st of Feb 2021.