There is a neat guide under the "How to play" button in the game, check it out.
Some "not so obvious" fact:
-You cannot win a map just by defending, you have to buy heroes at your war camp to raze the enemy castle!
-You have to buy the "Magic Tower" skill AND build a Magic tower on the map in order to use spells you have bought.
-Also there is two crucial spell under the Magic tower wich you dont have to buy, One of them give you more score the other is give
you more gold for killing mobs during the map.
-Your highscore is dependent only from your overall xp gained.
-The experiense gained dependent: how much mob you have killed and how fast you win a map. So you want to win quick, but still kill a horde of enemy (Next Round button is your friend), just don't overestimate yourself.
-There is a fast forward and pause button at the top right corner hidden under the "Highlord TD" picture :)