이렇게, 저렇게, 그렇게, and 이, 저, 그.
Simply put, 이 is "this"; 저 is "that"; and 그 may be related to "so"(그렇게), "such"(그런), or "it" (그것).
이렇게, 저렇게, and 그렇게 follow the same concept.
이렇게 is the easiest to understand, like "this way" or "like this".
It implies the speaker is doing something himself or referring to a physical or conceptual thing on or about himself.
It can mean something both of them are involved with, but the requirement is that the speaker is in the main role.
저렇게 is usually about something located away from but still in view of both the speaker and the listener.
그렇게 has two major uses.
The first is to refer to something about the listener.
The second is when the speaker (and the listener) can't see it, like a past experience or something imagined.
- 이건 이렇게 하면 돼. (The speaker demonstrates it himself to show the listener)
- 이렇게 열심히 일한 적은 없다. (more conceptual but still about what the speaker did himself)
- 저건 저렇게 하면 안 돼. (Referring to a third person away from both the speaker and the listener)
- 그건 그렇게 하면 돼. (Referring to what the listener is trying to do)
- 그 일은 그렇게 열심히 했는데도 안 됐어. (Referring to a past occurrence)