yup, hook it up to the left channel, listen to your left side. Unplug it, plug it into the right side, listen to your right side.
You could run a Y cable from left and right into one monitor and listen to each side by switching the outputs on the hardware or the software but I really don't know why you would want to.
Here's the thing, stereo is two mono signals. This stuff isn't complicated. SO, if you're doing mixing with maybe one item panned -10 left and something else +10 to the right just for a bit of spread, **** use one monitor if you want. You're pretty much just making a glorified mono signal anyway. But if you start using panned stereo delays where you echo between the two speakers or a flange or phase that "moves" across the speakers then you'll need two to hear that effect.
A good test would be listen to your music with one side of your headphones only, then switch. If you can't hear any difference from one side or the other, mix with one monitor. It won't make a difference.
Honestly, ADuB20 nailed it. That's the only reason they are sold as one item.