さて is a discourse marker that you use when you want to change the subject, start a new phase of conversation, or begin an action. It's like saying "Well, now" or "So then" in English. For example, after finishing a discussion, you might say さて to signal that you're moving on to the next topic. It is also used when you are about to do something, like starting work or giving instructions.

It is important to note that さて is not used in casual chat between friends as often as in more structured contexts like formal speeches or when you're in a role like a teacher or a boss. It's a bit formal and gives a sense of 'now, let's get down to business.' It's also used in writing to transition between paragraphs.

Be careful not to overuse it in everyday conversation, as it can sound a little stiff. Use it when you really need to clearly mark a change in direction.