Read about page numbers. This is important if you are going to use Word much.
Page Numbers in Word 2007-2016

There are at least three ways that Word gives you to insert automatic page numbers. The one they make most obvious is often the wrong way. Insert > Page Number and then in a location. That will always replace the current header or footer! I almost never use it.

Insert > Page Number > Current Location will put one wherever you could be typing text. However, unless that is in a header or footer, it will only appear on the current page.

Alt+Shift+P will insert a page number formatted in the Page Number character style at the current location.

The cleanest way to insert one at the current location is to press Ctrl+F9 and then type page and then press F9 again.

Another method (seldom used) is Insert > Quick Parts > Field > Page. That also inserts a Page field and lets you set formatting options.

If you start doing anything different with headers or footers, that can change the page numbering display.

Starting on a specific page - simplest way is to have that page be the beginning of a new section and format the page number to restart at 1 there.

Sorry, my inner geek grabbed the keyboard.