Im new to godot and i want to create a rts game like Kingdom and castle
Is this possible in godot and are there any beginner guides how the engine is built and introducing to gd script?
Cheers
Yes, it is definitely possible 
We usually recommend the official guides and documentation:
If you prefer videos, I suggest checking out GDQuest’s channel on YouTube.
More specifically, regarding “how the engine is built”, not sure what you looking for but here is some more advanced and techcnical information (see the links at the end of the page):
And as for learning GDScript: