Урок 45. Относительные местоимения. Часть II. Lesson 45. Relative Pronouns. Part II.

As well as being interrogative prionouns,  что (what) and ктo (who) are also used as relative pronouns.
(А) Что is used as:
- a relative pronoun to всё (all, everything): У меня есть всё, что надо - I have everything (that) I need.

- it is also used with то (that) to link two parts of a sentence. Notice that both тo and чтo must decline according to the context:

Я расскажу вам о том, что я знаю.
I'll tell you about (that which) what I know.

Мы начнём с того, чем мы занимались вчера.
We'll start with what (literally 'from that which') we were busy with yesterday.

- it is used to 'sum up' a previous part of the sentence (i.e. it links up to the whole of the preceding clause):

Он рассказывал нам о своей поездке в Африку, что было очень интересно.
He told us about his trip to Africa, which was very interesting.

(В) Кто is used as a relative pronoun:

- after тот (the one...):

Тот, кто хочет прийти на вечеринку.
Whoever (literally 'the one who') wants to come to the party.

- after всe (everyone):

Я приглашаю всех, кто хочет прийти на вечеринку.
I invite all who want to come to the party.

Notice that ктo is always followed by a singular verb (as it is in English).