Feudal economics

Most lands in Scarterra are agrarian, so most feudal lords manage parcels of farmland but lords can hold domain over all means of land capable of producing income selling not just crops but fish, timber, minerals, and reagents.
Normally, a knight's fief is likely to generate between 1000 and 3000 gold pieces worth of goods every year. That's usually enough money to replace his horse, armor, and weapons. You can usually tell the relative status of a knight by the quality of his horse, armor, and weapons.
Most barons and baronesses typically have land that generates between 3,000 and 8,000 gold pieces worth of goods every year.
Most counts and countesses have land that generates between 5,000 and 12,000 gold pieces worth of goods every year.
Most dukes and duchesses have land that generates between 7,000 and 25,000 gold pieces worth of goods every year.
Most kings and queens have a personal demesne that generates between 15,000 gold and 100,000 gold pieces every year.

From lowly knight to mighty king, you can usually estimate the ransom value of a captured nobleman by the annual income of their personal fief.

Execution

It almost goes without saying that not all realms are equal with some nobles controlling land much richer or poor than their norm for their status. Sometimes kings bestow honorary titles without bestowing accompanying land, but most people don't take these titles seriously, except with honorary knights as honorary knights are usually seasoned adventurers and thus very formidable.
Not only are all realms not equal, but rulers are not always equally good at managing their fiefs. Two nearly identical parcels of land will generate vastly different amounts of income if one of them is run by a competent manager and the other is run by a neglectful or wasteful manager.

Participants

Most Scarterran realms are patriarchal to some extent though less so than real world Earth in the medieval era. Most nations have titles pass to male heirs only, and the lord's word is law.
In many cases, especially in martial realms the lords duty is primarily the defense of the realm and the day-to-day operations are primarily overseen by the lady of the household. Nearly every human realm has the lady running the fief in her husband's absence but many have the lady running the realm even when the husband is there.
Sometimes, especially for the higher ranks like dukes and kings, a hireling actually runs the realm. This is individual is typically called a bailiff.