And you recive silver for showfights (the count of a shire can proclaim one from nation chests money) - that are duells with at least 100 VP on a specific shire. (25 Silver are possible for the winner)

And you recive silver when you are in a army thats conquers an enemy field with buildings or fiefdoms on it. (All plundered silver is divided between all attacking knights (of the winning army) equaly - could also be 20 silver or even more )

Also you can get some silver by quests (that other knights can give you) not much but 5 silver are possible (paid by the questgiver)

ANNNNDDD you can sell ressources from your fiefdom (e.q. Trade)

that should be everything

But your most money will be paid by your fiefdome in the long run so its usefull to build it up ^^