Write your programme to do the following
a) Manually input set points for temperature and humidity
b) Measure temperature and humidity (measured variables)
c) If measured variables equal set-point then motor drive = zero
d) If measured variables exceed set point then drive motor clockwise
e) If measured variables are lower than set point then drive motor anti-clockwise
You can add a further function in that the motor speed is set as a function of the error between setpoint and measured variables. This can be achieved by using a PWM output.
Edit : And once you have that up and running you can also introduce Integral and derivative functions so you end up with a fully operational PID controller.
As others have said you will need an H-drive
Be aware that you cannot drive a DC motor to a known position unless it has some form of position sensor fitted. If you do require predetermined positions you need to use a servo motor.