The Thrones - have an imbedded "help throne" function which will list the relevant commands.
The Lord - holds one castle. May be an underlord to another, or an overlord to others, but not both.
The Consort - may accept oaths of fealty.
The Knight - is a distinguished warrior.
The Mage - is a distinguished wizard.
The Castellan/Chatelaine - may pay taxes, add and remove residents, yet has no title unless they are also the consort, knight, or mage.
The Vassals - The more and better you have, the better. A vassal may have only one lord. They may find a new lord, renounce their fealty, or allow it to expire after a common year. The Challengers - hope to have more and better vassals than the lord.
The Lord's Taxes - must be paid at the Citadel in Soriktos or the castle may fall into ruin.
The Vassals' Taxes - are up to the Lord to collect.
Second Characters - won't help your cause - have fun trying.