The Civ's AI is a pretty broad area. You may take a look at
https://forums.civfanatics.com/threads/real-strategy-ai.640452/post-15324159 to better understand how the core system work. Behavior trees manage tactical level and are more difficult as there is virtually no documentation. Those two tables contain actual definition of the trees, the first contains the trees (nodes and relations) and the 2nd all required params.
Edit. Actually you should first check the table
NodeDefinitions. There are short comments on what each node does.