Couched lance - how do i use it effectivley?

[PersianPaladin]

I have recently acquired a lance as a weapon for horseback riding, but i have no idea how to use it. I notice that enemies sometimes give me 'couched lance damage' but i have no idea how to do that. Also whenever i press the button to attack with my lance, the enemy just blocks with their shield. I try to cause damage with my lance but instead i just run over the enemy with my horse. How do u cause couched lance damage?

 

[Lost-Lamb]

Fuc-.... I mean FaQ....