STEP 1: GO TO SOME RANDOM METROCOP
STEP 2: ASK HIM FOR A CAN
STEP 3: THROW THE CAN ON THE METROCOP'S HEAD
STEP 4: RUN
STEP 5: DR. BREEN WILL SEE YOUR ACHIEVEMENTS AND SHOULD KICK YOU TO NOVA PROSPEKT
STEP 6: EAT THE HEADCRAB
STEP 7: YOU ARE TURNED INTO AN OVERWATCH SOLDIER

CONGRATULATIONS, YOU HAVE COMPLETED THE TUTORIAL