What is the meaning of -고?

and then, after...; marks successive action.

and; connects two clauses together.

Used for the main verb to join it to certain auxiliaries.

In the intimate style, used to ask confirmatory questions; by extension, can have nuances of denial or sarcasm.

In the intimate style, used in polite requests.

In the intimate style, used to present additional information, typically with the nominal particle (-do, also, too).

that; quotative particle marking indirect quotes. Attaches to mood-marking verb-final suffixes of the "plain style".

In the intimate style, a particle attached to verbs to request confirmation of what the speaker has just heard; by extension, can express surprise about what they have just heard.

In the intimate style, a particle attached to verbs to emphasize that the speaker is repeating something they have just said; by extension, can be used to express emphasis or annoyance even if one is not actually repeating something.

Used with the declarative in certain constructions as 다고 (-dago); see there for more.

Used to join the verb expressing the desired action to 싶다 (sipda, to want).

In the plain style, an interrogative suffix marking wh-word questions. It is only used for the copula 이다 (-ida, to be) and 아이다 (aida, to not be).

See above; sometimes appended directly to the noun, as in older forms of the language.

Source: wiktionary.org