A THREAD FOR NEWCOMERS!

Could you please advise which faction has the best starting army for clearing territory with minimal losses on the way to the enemy city and capturing the city itself?

It varies. But if you want to avoid losses, I would recommend Necropolis and Galthran.

Which level 1 and 2 spells are the most effective? And on whom should they be cast?
What are undead? Are they living creatures?

It is generally accepted that the most useful schools of magic are Earth and Air. Earth because of slowing, Air because of speeding up. Water (blessing + healing) also looks good, in my opinion. As a last resort, Fire (bloodlust, curse, blindness) can be used. On whom to cast what - it depends on the situation. Undead are the "inhabitants" of Necropolis + mummies. This classification is described in section 2.4 of the Physics and Magic Guide.