Whom

WHOM:  

Whom is the objective form of 'who'.

It is better to use it along with 'to','for','with' or 'by'.

Examples:

1. For whom are you waiting?
2. With whom have you gone for shopping?
3. To whom did you send the message?
4. By whom was this boy beaten?

Note: Modern grammarians use 'who' and find it more appropriate than 'whom' in other places.