If you press Tab, it'll give you an overlay with key bindings on it (there was a prompt for that during the tutorial fight).
By default, left mouse button is dodge (for heavy attacks) and right mouse button is guard (for light attacks). The rest of the combat options are controlled via WASD.
It looks like bindings can be changed from the Options->Commands from the main menu (you'll need to press Escape, Save & Exit to get back there, and then you can hit Continue to resume your game).
Hope that helps!