"Take a backup" just means to make a copy of the original Normal.dotm file, so you can restore it if the procedure doesn't solve the problem. That file contains many of the customizations you may have made in the program, and you probably don't want to lose
those.
It doesn't really matter what you rename the file to, as long as it isn't "Normal.dotm". I'd suggest "Normal_Old.dotm", but you could name it "Maybe Buggy Normal Template.old" and the result would be the same. The point of this is that, if Word runs and
doesn't find a file named Normal.dotm in the Templates folder, it will use all its default settings from within the program; and when you exit from that session, it will write a new, factory-default Normal.dotm into the Templates folder.
If doing this makes the prompts stop, then you can use the Organizer to copy any custom styles and/or macros from the old template to the new one. To open the Organizer, press Ctrl+Alt+Shift+S to open the Styles pane; click the Manage Styles button (third
from left at the bottom of the pane); and click the Import/Export button. In the Organizer, click the Close File button on the left side, and click it again when it says Open File. Select the old template (the new template is already displayed on the right
side). Select any styles you want on the left, and click the Copy button. Repeat for macros on the Macro Project Items tab of the dialog.