Do is a verb meaning to complete or perform an action. A to-do list is something that outlines all of the things one needs to accomplish in a certain amount of time.
Another phrase is the dos of something or the things that are good or correct to perform within a certain area. Do’s is a sometimes accepted spelling variation. The preferrence between the two spellings depends largely on the type of publication one is writing for.
Dos or do’s are accepted plural spellings of the word do when it means an event or party. This is informal slang and used mostly in British English.
Note here that ‘dos is American slang for the word hairdo.
Getting people and firms to spend more, bringing more people into the labor force and improving productivity are Mr. Cox’s three do’s for achieving this. [The Wall Street Journal]
That comes through Laverne Cox’s character, Sophia, who plays a stylish fairy prison godmother, sprucing up many of the women with fresh new ‘dos while providing them with much needed confidence. [Mashable]
The insider went on: “The other option, of course, is to have two dos – a small, private family affair and then a big beachside bash for everyone to have a few drinks and a bit of a party. [Entertainment Wise]