Calogrenant is knocked off his horse by the other knight's lance. A lance was a long wooden spear with a sharp metal point. When knights fought, they would charge at each other on their horses from as far away as possible. They would try to spear each other with their lances or knock each other to the ground. A knight had to protect himself with his shield with one hand while trying to use his own lance against his enemy (as well as steering his horse).
Still,
lances weren't much use after the first charge - they often broke in the clash
and were difficult to use in close-up fighting. So then the knights would
fight with swords, standing up in their stirrups and hammering at each other's
helmets or trying to cut through each other's mail.
If one knight fell from his horse, the other was supposed to get down too and they would carry on fighting on foot. If the loser was not killed, he often had to declare himself the prisoner of the other and do what he asked.
Sometimes knights would fight as entertainment for other people to watch. These pretend fights were called tournaments.
Two knights might fight each other alone (this was called single combat) while a huge crowd watched and cheered. Or else a large number of knights might form two teams, like two enemy armies, and try to beat one another at jousting (fighting on horseback with a lance) and sword-fighting.
Ladies often gave favours or tokens (a scarf or a flower or part of their sleeve) for their favourite knight to wear. Sometimes they would be the judges, deciding who had fought the best and giving prizes.