Stronghold Kingdoms is a free to play game. There are no premium subscription accounts.  Players can however play a Premium Token that gives them access to extra features for a period of time (2, 7 or 30 days) that can be very useful:

• Extra building queue slots
• Extra research queue slots
• Move village buildings
• Villages overview page
• Offline auto-trading
• Offline auto-scouting
• Offline auto-attacking
• Offline auto-recruiting
• Vacation mode

NOTE: A Premium Token only effects the world on which it was put into play

For more information about Premium Tokens and a more detailed explantion of the extra features, please visit the wiki: http://help.strongholdkingdoms.com/index.php/Premium_Tokens