Pick the layout you want - with legal drafting, the standard pagination is a simple Arabic numeral at the bottom center of the page. To add page numbers, View > Print Layout > Document Elements > Page #.
Once you are done editing, click the red 'Close Header and Footer' button at the top of the page to leave it and go back to the main document text. You may also need to access the Footers when setting up your sections in your document.
Assuming you placed the page numbers at the bottom of the page - in the footer - Insert > Footer > Edit Footer. Once you have inserted page numbers, you can always go back and edit or remove them. You can also use this same dialog box to change the page numbers to lower case Roman numerals, letters, etc. To start with a number other than '1', choose Insert > Page Number > Page Number Format > Start At (then select the page number you want to start with). Word will give you several different formatting options, but typically in legal writing, it is best to stick with simple formatting. Then choose whether to place at the top or bottom of the page (the standard placement in legal writing is at the bottom center of the page). To insert basic page numbers, Insert > Page Number.
