Connects a reason or preceding context to a natural result or next action. Common in both spoken and written Japanese.
It started raining. So the game was canceled.
昨日はとても疲れていた。それで、早く寝た。
I was very tired yesterday. So I went to bed early.
The train stopped. So I was late for work.
So what happened? Did she end up coming?
それで links events as 'and so' and can also imply a reason ('because of that'), whereas すると just marks the next event as a natural consequence without implying causation.