It's useful to note that this forum provides a "Histogram" button at the bottom-right corner of an embedded image. Click on the image, hover the pointer in the bottom-right corner, then click "Histogram."
With that tool in hand, let's see some real-world examples. OK, maybe not real-world, welcome to MY world 
1. This image is properly exposed. That is, the skin tone is exactly where I want it, and all the important details are clear and visible. Take a look at the histogram.
[Main light is an Elinchrom D-lite with the Maxi-Lite modifier; kicker light is two bare Speedlights, one clamped to each side of the backdrop stand. The blue is an LED stage light that I didn't think would have so much of an impact on the shot, oops]
IMAGE LINK: https://flic.kr/p/vgv7eT
BBB_Cabaret_20150626_8711.jpg
by
Nathan Carter
, on Flickr
2. This image is properly exposed. That is, details in all the important areas are visible, and the background is so brightly exposed that most detail is lost - which is exactly how I wanted it. The skin is correctly exposed (though my processing added a lot of saturation). Take a look at the histogram.
[Main light is a 430EXII in a cheap brolly box; background is lit by two bare Speedlights]
IMAGE LINK: https://flic.kr/p/pRNgwx
Moxie_20141005_30359.jpg
by
Nathan Carter
, on Flickr