Place the cursor where you want the line
Type three hyphens and press Enter to insert a straight line
Type three underscores and press Enter to insert a thicker line
Type three equal signs and press Enter to insert a double line
Type three asterisks and press Enter to insert a dotted line
Go to Insert
Select Shapes
Choose the line shape
Draw the line across the page
Go to Home
Select Borders
Choose Horizontal Line
Right-click the line to format or remove it