What it means
なさる is the plain-form honorific equivalent of する. It respectfully describes an action performed by a person who deserves respect, such as a teacher, manager, customer, or other senior person. It is often attached to a verb masu-stem, as in 掃除なさる, meaning “to clean” respectfully. The polite form is なさいます, used when the whole sentence is in polite speech.
Usage note
なさる is honorific, not the ordinary polite counterpart of する. Use します for ordinary polite speech, and use なさる or なさいます when respectfully describing someone else's action. Do not normally use it for your own actions.
How to use it
先生は毎朝、庭を掃除なさいます。
The teacher respectfully cleans the garden every morning.
先生は毎朝、庭を掃除なさる。
The teacher respectfully cleans the garden every morning.
Example sentences
館長は毎週土曜日に図書館を掃除なさいます。
The library director respectfully cleans the library every Saturday.
校長先生は来月の式であいさつなさいます。
The principal will give a speech at next month's ceremony.
部長は午後に新しい計画を説明なさいます。
The department manager will explain the new plan in the afternoon.
先生