Place the cursor where you want the line
Go to the Home tab
Click the Borders drop-down in the Paragraph group
Select Horizontal Line
Type three hyphens and press Enter
Type three underscores and press Enter
Type three equal signs and press Enter
Type three asterisks and press Enter
Insert a line from Insert tab by selecting Shapes
Choose the Line shape and draw it in the document
Use the keyboard shortcut for a horizontal line if available in your Word version
Adjust the line using the Format or Shape Format tab if needed