Use of 'what' :
1. asking for information about something - What is your name?
2. asking for repetition or confirmation - What? I can't hear you.

Use of 'when' : asking about time - When did he leave?

Use of 'where' : asking in or at what place or position - Where do they live?

Use of 'who' : asking what or which person or people (subject) - Who opened the door?

Use of 'whom' : asking what or which person or people (object) - Whom did you see?