Based on the type of document you want to create, you must first select the page

A. Size

Explanation:

The question is about Microsoft word, and the following options are missing:

A. Size

B. Orientation  

C. Margins

D. Style

The first you have to select is the page size because size "dominates" orientation and margins, that is, the orientation and the margins have sense only relative to some size.

You only have to worry about style after you finished your text.