The normal basic PWM has a N channel mosfet,so the negative of the motor is connected to the 'drain' of the PWM,
the positive is common to both the motor and PWM+ ,the negative (ground) is connected to the 'source' of the PWM. Bear this in mind:- the case of the mosfet is physically connected to the 'drain' pin of the mosfet, so the heat sink should NEVER be grounded. The current is adjusted by the potentiometer that is installed on the PWM circuit board,or by remote if you extend the wiring from it.An analogue ammeter can be connected in series with the negative supply.If you intend to use a digital ammeter, a shunt must be used if the ampage exeeds the rating of the meter. I could create a diagram if you need one. Give some indication as to what device you are controlling,
voltage,max current draw ect; If you intend to run the appliance at the constant maximum ampage,you will need to make sure the PWM is suitably rated to cope.