Who Whom Whose

To understand how to use 'who', 'whom' and 'whose' you first have to understand the difference between subjects, objects and possessives.

The subject does the action:
He likes football.
She goes to university.
They enjoy travelling.

The object receives the action:
The employees respect him.
I know her.
The sailors waved to us.

Possessives tell us the person something belongs to:
His car is new.
I like his latest novel.
We returned to our hotel.

'Who' is a subject pronoun like 'he', 'she' and 'they'. We use 'who' to ask which person did an action or which person is in a certain state.
Who wrote that letter?
Who is the manager?
Who is going to prepare dinner?

'Whom' is an object pronoun like 'him', 'her' and 'us'. We use ‘whom’ to ask which person received an action.
Whom are you going to ask to the party?
Whom did they choose as team captain?
Whom did they summon?

'Whose' is a possessive pronoun like 'his', and 'our'. We use 'whose' to find out which person something belongs to.
Whose phone is this?
Whose is this umbrella?
Whose car is blocking the drive?