First, using the Insert tab in MS Word, select Page Number (not Header), Top of Page, then Plain Number 1. This will insert a running page number on the top left of your header.
Second, your cursor will be blinking to next to the 1 you have inserted. Type several words from your title there, using all caps.
Last, on the far right of the tabs window, find the Insert Tab Alignment tool (under the Tabs & Alignment Tools, Position submenu). Select it and an Alignment box will appear. Select the Right alignment option and click Okay. The page number will jump to the right and your title for the Running Header will stay aligned to the left, in good APA
Beside the page number, simply type your last name. Then click out of the header, and you are done. The name and page number will run on each page you create as you write your paper.