てください

1. 1Asks or instructs the listener to do an action politely: 'please do ~'.Ex. 2
2. 2Politely invites or encourages the listener to do something that benefits them, such as sitting down or helping themselves.Ex. 1

A standard polite request used in everyday conversation, classrooms, shops, signs and instructions. It is polite but still direct, so it often works as an instruction, for example from a teacher or staff member. Softer, more tentative requests use ていただけませんか, gentle invitations use ませんか, and the negative request 'please don't' is ないでください.

• ていただけませんかN4ていただけませんか also attaches to the て-form, but it makes the request as a negative question, which is more humble and indirect than てください — suitable for superiors, elders, or customers. It cannot replace てください in the どうぞ 'help yourself' usage.
• ないでくださいN5ないでください means the opposite: please do NOT do something. It attaches to the ない-form plus で (never なくてください), and is also common in signs and rules expressing prohibition. The two are not interchangeable.
• なさいN4なさい attaches to the ます-stem and is a command from a superior to a subordinate, typically used by parents to children, teachers to students, or in exam instructions. It cannot be used with customers or superiors (greetings like おやすみなさい excepted) and has no 'help yourself' usage.
• てほしいN4てほしい states the speaker's wish: you can want someone to do something (the doer marked with に or が) or want a situation to be so, as in 病気が治ってほしい. When used to make a request, it sounds softer than てください.
• させてくださいN4させてください asks the other person to let you (or your side) do something, as in 行かせてください or 考えさせてください, while てください asks the other person to do it. The former uses the て-form of the causative, so the two are not interchangeable.
• ませんかN5ませんか attaches to the ます-stem and is mostly used to invite someone (often to do something together with you), leaving the decision to them, which sounds more indirect. てください attaches to the て-form and is a request or instruction for the other person to comply with.

てください is a direct polite request: ていただけませんか is a softer, humbler question, ませんか is a gentle invitation phrased as a question, either to join the speaker or for the listener to act (こちらに座りませんか, 'Would you like to sit here?'), and なさい is a firmer command from someone in authority. ないでください asks someone not to do something, てほしい states the speaker's wish for someone to act, and させてください asks permission for the speaker to do something.