The words whoever, whatever, whichever, however, whenever and wherever are called compound relative pronouns. These are used to mean ‘it doesn’t matter who/what/which etc.’

A compound relative pronoun has a double function. It acts as a subject, object or adverb in its own clause; it also acts as a conjunction joining its clause to the rest of the sentence.

Whoever comes to the door, ask them to wait.
Whatever happens, happens for good.
Whoever phoned just now was very rude.
Don’t open the door whoever they are.
Wherever you go, I will follow you.

Stay cool, whatever happens.
Whichever of them you marry, you will land in trouble.
However much she eats, she never gains weight.
Whenever I go to Bangalore, I try to spend a few days with my grandparents.

Informal uses

In an informal style, these conjunctions are sometimes used as short answers.

‘When should I come?’ ‘Whenever‘. (= Whenever you like)
‘Tea or coffee?’ ‘Whichever’. (= I don’t mind.)

Whenever can suggest repetition, in the sense of ‘every time that’.

Whenever I go to Singapore, I stay with my sister. (= Every time that I go to Singapore, I stay with my sister’)
Whenever I see you, I feel happy.