This is a conjunction that connects two sentences. After you describe an action or situation in the first sentence, you start the second with そうすると to say what happens as a result or what you should do next. It carries a nuance of 'if that is done' or 'once that happens', and the result is often a natural consequence or a logical next step.

In conversation, it can also be used to say 'and then' when narrating a sequence of events, but it's slightly more logical than simple そして. It frequently appears in explanations, instructions, and storytelling. In writing, it's common in both formal and informal texts, but in speech it's natural too, so you can use it without worry.

Be careful not to overuse it in casual chat; it can sound a bit explanatory. Also, it's not the same as そうすると as a condition ('if you do that') vs そうしたら which is more colloquial and common in everyday conversation for the same meaning.