Use the correlative construction тћ, как to introduce time clauses.
There are various ways of expressing the fact that two events take place in a particular sequence:
  1. You can join two sentences with 'and', e.g. 'He ate dinner and left.'
  2. You can introduce one sentence with a temporal conjunction, e.g. 'After he ate dinner, he left.'
  3. You can use a preposition + noun, e.g. 'He left after dinner.'
  4. You can use a deverbal construction, e.g. 'Having eaten dinner, he left.'
These four ways exist in Russian as well as in English, but methods (2) and (3) differ from each other in Russian. In English, prepositions [as in (2)] can be used to introduce clauses [as in (3)], but in Russian they cannot. In Russian, clauses must be introduced by clause introducers, not by prepositions.
Clause introducers include single words like как, что, котћрый, as well as two-word combinations called correlatives.
The correlative construction for introducing clauses that refer to time (like 'after he ate dinner') consists of the appropriate form of тћ plus the uninflected word как (пћсле тогћ, как ћн пообљдал).
In the correlative construction meaning 'after', you use the Genitive form of тћ (тогћ) after the preposition пћсле just as you use the Genitive form of обљд (обљда) in the prepositional phrase пћсле обљда 'after dinner'. Compare these four ways of expressing the same sequence of events:
  1. Ћн пообљдал и ушёл.
  2. Пћсле обљда ћн ушёл.
  3. Пћсле тогћ, как ћн пообљдал, ћн ушёл.
  4. Пообљдав, ћн ушёл.