Idle + Mouse1 = Quick Attack (Fast attack low damage)
W + Mouse1 = Stab
S + Mouse1 = Back Stab (Attack opponent from behind)
A + Mouse1 = Swing to left
D + Mouse1 = Swing to right
W + A + Mouse1 = Diagonal chop / downwards from right
W + D + Mouse1 = Diagonal chop \ downwards from left
A + S + Mouse1 = Diagonal uppercut swing / upwards from left
D + S + Mouse1 = Diagonal uppercut swing \ upwards from right
Ctrl + Mouse1 = Special Attack
Input for the commands is newb friendly, if your strafing right, you will automatically perform (D + Mouse1) which will Swing to the right, much like you would expect.
EDIT: Another example, say you wanted to swing left while running right, you can press A + Mouse1, then press D while the attack is being performed.