Could anyone be a knight?
There were two ways to become a knight. The first was to be born the son of a knight or other royalty. At a certain age, the son would start learning the trade.
The second way to become a knight was for a man not of nobel birth to show bravery and loyalty in battle. The lord or king would make the common soldier a knight. This was not very common, though, because usually it took a long time and a lot of money to learn how to become a knight.