I have one that I haven't used for ages.
First off--Don't turn it on in room light. This can damage the sensor. Only turn it on in the darkroom under the enlarger.
The basic idea is that you start by making a good print with tones that you want to reproduce in later prints (skin tone, neutral grey, sky blue, etc.). I recommend owning a set of print viewing filters for judging filtration from a dry print.
You calibrate for each tone by putting the sensor on the easel, probe toward lens, with safelights off if you use them, reading the calibration tone. Set the probe for each channel (CMY) and zero out the meter with the corresponding dials (if I remember correctly--it may be that you set the dial so that the meter reads the filtration value), and note the exposure time on the Black channel. Write down the dial settings and exposure time for each calibration tone.
Now, when you get a neg or slide with that tone that you calibrated for, you dial in the settings you wrote down, read the tone on the easel with the probe toward the lens, just like you did for calibration, adjust filtration to zero out the meter for each channel and adjust aperture to get the exposure time you wrote down earlier (or adjust exposure time, if you don't get an aperture value that you like), and you should be pretty close.
You can use it with just the black channel for B&W as well.