Start out first with just reducing some balsamic - it's really good stuff. Once you taste it you will know if there was anything else involved.
Yes, just put some in a VERY small pot on about medium or so. Once it starts to thicken remove it from the heat. It will continue to thicken a bit. You don't want to have to chew it!
It's GREAT drizzled on fresh Brussels sprouts, cut in half. First drizzle with olive oil, sprinkle with kosher salt, drizzle with the balsamic, roast in oven on about 375 until they are browned and roasted but not crispy, of course.