You're teaching a coworker how to use a database application. You're explaining how to fill in an important form. You notice that something changed on the screen, so you point it out to your coworker.
You're in a meeting at work. One of your coworkers makes a suggestion. You don't like the suggestion, so you politely reject it.
You've been hanging out at a friend's house on a Saturday afternoon. You've been there for several hours, so you feel like it's time for you to leave. You say this to start leaving.
You're watching a movie with your friend and you didn't understand something that a character said. You ask your friend this, hoping he can clear up the confusion.
You call a client's office. The client isn't there, so his assistant answers and offers to take a message. You say this because you don't want to leave a message.