直（なお）す is a verb that means ‘to fix’, or ‘to redo’. It is used when saying that something needs to be done a second time (usually due to the result/quality being insufficient the first time). To use 直（なお）す, it will need to be attached to the ます stem form of any verb.

• 髪（かみ）がちゃんと染（そ）まってなかったので染（そ）め直（なお）します。
  Because my hair isn’t properly dyed, I will redo it.
• フェンスを塗（ぬ）りなおす。
  To repaint the fence.

With する verbs, the conjugation rules are slightly different. する will become し, and then 直（なお）す will be connected in the regular fashion. In some situations, する may be replaced with やる (a very casual equivalent of する). As やる is a う-Verb, it will be conjugated as やり直（なお）す.

• お客様（きゃくさま）に挨拶（あいさつ）をし直（なお）す。
  To re-greet the customer.
• プロポーズはやり直（なお）す事（こと）が出来（でき）ないから、緊張（きんちょう）している。
  Because you can't redo proposals, I am nervous.