The gridlines make it easy for you to align objects with other objects, or align up to a particular spot on the page. The gridlines by default are off to make the reading easier, but you can always bring them back when you need them. Please see below for details:
Step 1: Click the "View" tab from the ribbon;
Step 2: Check the "Gridlines" box in the "Show" area;
Step 3: The Gridlines will display in the word file.
Step 4: If you want to hide the gridlines after, please repeat the same steps.
In Excel, if you need to hide or show the gridlines, you can use the exact same steps.
One difference is that by default the gridlines do not show in Word but show in Excel.
If you are familiar with the Google sheets, you can also use similar steps to hide or show the gridlines.