〜てください

て-form + ください makes a polite request: 窓を開けてください, "please open the window"; ちょっと待ってください, "please wait a moment".

It's polite, but it's still telling someone to do something, so it suits instructions, directions and everyday favours. Teachers, doctors and signs use it constantly.

Among friends, the て-form alone does the same job: ちょっと待って! "hang on!"

For more delicate requests, adults soften it: 開けてくださいませんか ("would you mind opening it?"). And for "please give me" a thing, it's noun + をください, which you've already met.