Request
てください
It is a polite request that is translated as “please do”. See Conjugation Basics (“command”). In casual speech, can be shortened to て.
Example
消しゴムを貸して。 Lend me your eraser.
てもいい
V-て
い-Adj い くて
な-Adj + で
N + で
+ もいい
Means “is it alright if?”, “may I?“.
Example
ここに座てもいいですか。 May I sit here?
A more polite way is ても構わない.
ないでください
Means “please don’t”. It is a polite request. Removing the ください makes it more casual. Formed by a verb in the negative form (ない) with the で particle.
Example
冷蔵庫のデザートは食べないでください。 Please do not eat the dessert from the fridge.
なさい
This form is used when commanding an action. It is used with verbs by removing the ます and adding なさい. In casual conversation, it can be shortened to な.
Example
質問を答えなさい。 Answer the question.
ように言う
It means “to tell”, “to request”, “to order”. It is form by added ように言う to a verb. The verb 頼む can be used for requests, while 命じる can be used for order. The verb 言う can tell the three meanings depending on the tone.
Example
子供にお菓子を食べないように言った。 I told the kids to not eat candies.