seems you are on a steep learning curve.
as you know we perceive in analog, a rotating bicycle wheel moves in analog.
an electric motor on the other hand moves in pulses, or digital.
your part, the *USB-1208-LS *seems to be an analog INPUT device so you can read and input.and has multiple INPUT channels and 2 OUTPUT channels.
putting your project aside for a moment
a DAC is a digital input, Analog output circuit, device or chip. digital to analog.
if you want to light an light bulb, you can use a microcontroller like the Arduino send out pulses.
imagine that if over the course of 1 second, you sent out 1,000 pulses. the pulses where high half of that second.
if you were controlling a lamp, then the lamp would be lit for half of the time. it would appear to be half bright.
it would get the full power, in pulses, but only half the time. the pulses would be so fast you would not perceive that the light was off half the time.
this is digital. we can control the PULSE, and if we always use 1,000 pulses per second, and we have each pulse ON for half the time and OFF for half the time, then the average would be 50%
If we control the width of that pulse and make the pulses ON for 3/4 of the time, then the apparent output would be be 3/4
Compare that to taking the same lamp and just giving it half the voltage. It would appear to be half bright.
give it 3/4 voltage then it would appear to be 3/4 bright.
to get those pulses the Arduino has that built it. called PWM or pulse width modulation. the number of pulses are fixed, we just modulate how wide they are.
to get that half voltage, you need lots of circuitry or special chips. that is a Digital to Analog Converter.
lots and lots of things can work with PWM.
some things require analog.
in our world , PWM is preferred, and easy to do, built in, free if you will.
DAC is specialized, requires more stuff and expensive.
this was a very casual explanation, lights are not exactly half bright at exactly half voltage or 50% pulses....
sometimes being casual makes it easier to understand the general concept.
as for your project, it may be super simple to use PWM.
if you have an output for a motor, we can tune that PWM to that motor, but it might not work for a light or a different type of motor, it may need to be re-tuned, or just incompatible.
the great thing is that lots of motors can take either PWM or variable voltage and work exactly the same.