I'm a newbie and bought this game on a recommendation from another forum.

I didn't have much time to spare, so I jumped in without reading the manual.

The tutorial is sparse, but functional, so I did not have much trouble. I really like that you can click on help topics for all of the missions!

However, two things threw me off:

I used worker units to rebuild a watch tower ruin... but, to rebuild other house ruins, I apparently needed my army to do so, not the worker unit. Very, very weird, and what is the rationale behind that? Is it historic reasons?

After capturing the capital, there are farms around it, which apparently are burning, even though the animations for it have disappeared. But the commands for both putting out the fire and rebuilding it are grey for both my army and my worker units, and there is no explanation as to why. What did I miss?

You're probably too early in the game to actually build anything. Sometimes a tooltip will pop up saying "Philip must confront Bardyllis before he can take on any massive building projects!" or something similar. As with the crop burning, you extinguish the fire to keep it from burning further, but the percentage stat at the bottom in the farm itself is a representation of how much of the crop is destroyed, not how "on fire" it is. You can't extinguish it further or rebuild the farm once it's just not on fire, you simply have to wait for the crop to regrow over the course of a year and for the "burnt out" percentage to die away.