Q. How do I add a running header in Word to an APA style paper?

For an APA header you need the title of your paper on the left, and the page number on the right.  Here is how to do it:

1. Go to the Insert menu in the Word ribbon. Select Header from the Header & Footer section.
2. Select Blank Header, the first option.
3. Click on Page Number on the top left.  Select Top of Page, then Plain Number 1.  The pages will now have the page number on them.
4. Type the title of the paper in all caps.  If it is over fifty characters, use a shortened version of the title.
5. After typing the title, place the cursor immediately to the left of the page number.  Press page until the page number is on the right of the page.

Below is a link from APA Style with guidance on running headers and sample papers to see how it is done.