There're many types of line in Word you can put in the document as a kind of separation. If you tend to use them frequently, it may not be the best way to add lines from the Insert tab every time. Therefore, I'd like to share some easier ways basically don't need mouse clicks.
1. Straight Line
The most common line in Word. To input it, just press "-" button in your keyboard for 3 times and then press Enter.
2. Double Straight Line
Input "=" for 3 time and then press Enter key.
3. Triple Straight Line
Input "#" (press Shift+3) for 3 times and then press Enter key.
4. Wavy Line
Input "~" (press Shift+`) for 3 times and then press Enter key.
5. Dotted Line
Input "*" (press Shift+8) for 3 times and then press Enter key.