Immediately means right now, without any delay or waiting. When your teacher asks you to sit down immediately, she means this very second, not in a minute or after you finish talking to your friend. When a doctor says a patient needs surgery immediately, there's no time to waste.

If you leave immediately after school, you walk out the door as soon as the bell rings. If you respond immediately to a text, you type back the instant you see it.

Compare this to words like soon or shortly, which suggest a short wait, or eventually, which means at some point in the future. Immediately means the gap between the request and the action should be zero. When something must happen immediately, it's often urgent or important: a fire alarm means evacuate immediately, and a referee's whistle means stop playing immediately.

Parents and teachers use this word when they really mean business. If you usually hear “please clean your room” but today you hear “clean your room immediately,” you know the situation has escalated from a suggestion to a serious requirement that needs your instant attention.