After the instructions on the screen fade away you can pause the game (p or esc) to see them again. Basically you create units by purchasing parts by clicking the buttons on the left. The top button is the unit frame, the square, circle, and triangle are parts that you drag onto the frame to create units. You can then drag the unit onto the field to defend your shrine from the enemy. You only have 30 seconds each round to create and update your defense. Once combat starts your units attack the enemy automatically.
Anyway, thanks for trying!