Rule 1. Who and sometimes that refer to people. That and which refer to groups or things.
Examples:
Sita is the one who rescued the bird.
Mohan is on the team that won first place.

Rule 2 - That introduces what is called an essential clause (also known as a restrictive or defining clause). Essential clauses add information that is vital to the point of the sentence.
Example: I do not trust products that claim "all natural ingredients" because this phrase can mean almost anything.