Missions are easy, you normally have to speak with someone to get information or to know what the people think about the kingdom or you have to buy things and work in your workshop.
You have to star with the Monarch because every realm needs a monarch. He normally has to solve the peasants' problems. Everyone must respect the monarch... if you don't want to have problems.
I played a lot with the physician (who is like a doctor). I don't want to look for many medieval words in the dictionary, so here is EA's description: The physicians uses leeches to drain the blood of the sick, preparing them to receive wondrous cures cooked up at the crafting table. It's fun to play with a physician.
And I played only a bit with the peteran priest. The peteran church is inspired in the romanesque monasteries and the priests attemps to gain believers by making popular sermons. They're like the good priests who say good things to the believers while the jacoban priests try to scare the people to gain believers: you'll die if you don't convert into the jacoban religion, for example. The jacoban church is inspired in the gothic cathedrals. Some shots of my peteran priest:
That's all for now. Happy simming!