type May 23 into cell A1
In the bottom right-hand side of the cell(when selected) is a black box,
click and hold with the mouse and drag it down to cell A3.
You will have the following
A1= 23-May
A2= 24-May
A3= 25-May
You can right click on the cells (when highlighted) and change formats to show whatever format you want-- 5/23, May-23, etc..
Let me know if you need anything else.