Note: The decision panel that appears once the siege camp is ready is similar to that of regular field battles, and you’ve experienced plenty of these in Mount & Blade II: Bannerlord. “Lead an assault” means you’re part of the attack and commanding your forces; “send troops” means you’ll let the AI handle the siege via auto-resolve. If the enemy still has a considerable force, auto-resolving isn’t advisable unless your Tactics skill is high enough. Since siege battles will often favor the defenders, it can lead to disastrous losses if you’re on the offensive.