You use so to refer back to something that has just been mentioned.

You use so when you are saying that something which has just been said about one person or thing is also true of another one.

You use the structures as...so and just as...so when you want to indicate that two events or situations are similar in some way.

If you say that a state of affairs is so, you mean that it is the way it has been described.

You can use so with actions and gestures to show a person how to do something, or to indicate the size, height, or length of something.

You use so and so that to introduce the result of the situation you have just mentioned.

You use so ,so that, and so as to introduce the reason for doing the thing that you have just mentioned.

You can use so in stories and accounts to introduce the next event in a series of events or to suggest a connection between two events.

You can use so in conversations to introduce a new topic, or to introduce a question or comment about something that has been said.

You can use so in conversations to show that you are accepting what someone has just said.

You say 'So?' and 'So what?' to indicate that you think that something that someone has said is unimportant.

You can use so in front of adjectives and adverbs to emphasize the quality that they are describing.

You can use so...that and so...as to emphasize the degree of something by mentioning the result or consequence of it.

You use and so on or and so forth at the end of a list to indicate that there are other items that you could also mention.

You use so much and so many when you are saying that there is a definite limit to something but you are not saying what this limit is.

You use the structures not...so much and not so much...as to say that something is one kind of thing rather than another kind.

You use or so when you are giving an approximate amount.