I will post a video walkthrough then, I wanted a better in-game tutorial but time ran out before I could implement it. Here's a written tutorial in the meantime: 

A hero is coming the raid the castle, with the objective to fight the boss(which is you). In the first half, you can move around and press Q to open the menu, then you can use the Funds to do the following:
Deploy units, which will take the hero's life, stamina and give more power to the lord. 
You can choose Block, which will block paths to make sure the hero will go the way you want him to go. There are three different crossroads, at the start, and on both sides, if you hover near these crossroads, the Block option in the menu will give the option to block any path there.
This is useful as, the longer the hero takes, the more Magic your character has, and also there are blue and red blocks around the place, which if the hero touches, it will power him up.
Finally you can spend Funds to improve the Boss's stats.
After you are done, Select the End option in the menu to advance, the hero will spawn and advance through the castle, if there are multiple paths available he will choose one at random, and fight any unit he touches, while he is walking, your Magic will go up.
Once he reaches the boss, a turn based battle will start, you start attacking, just choose any option as long as you have the resources to use them, which is Stamina and Magic. Once you attack, the hero will block, then he will attack and you have to choose one of the block options, afterwards you attack again, until one is defeated.  If you run out of stamina, you can choose do nothing to recover some during either attack or defense.

I hope it's enough to understand, I will post a video soon and if you have any other doubts or feedback feel free to post them.

Hey there and thanks for playing. The first part is tower defense, you can press Q to open the menu to deploy units and block paths, I guess I forgot to specify that Q was the button to open the menu, sorry about that, will update the description saying that, if you could try again afterwards it would be much appreciated.