THAT vs WHICH vs WHO
​'That is used with phrases that are 'essential' to the sentence - (known as Restrictive Clause).  A 'restrictive clause' is part of a sentence that cannot be left out because the meaning of the sentence would change its meaning if the clause were deleted.  A 'restrictive clause' is essential for the intended meaning.
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-  The umbrella that you lent me is in my car.
-  The house that I wanted to buy has been sold.
-  The Tesco that I go to is closed today.​
'Which' is used when it is considered that the phrase is 'not essential' to the overall meaning of the sentence and could, therefore, be omitted - (known as Non-Restrictive Clause).  A 'non-restrictive clause' is something that can be left out without changing the meaning of the sentence. These clauses are usually set off between commas.

-   The umbrella, which is brown, is in my car.
-   The house, which I didn't want to buy, has been sold.
-   The Tesco, which is near my house, is closed today.
'That' and 'which' refer to groups.
'Who' refers to people   -  Visit Who vs Whom