Video: Binary and hexadecimal are a bit baffling at a glance. The idea that a computer uses numbers and letters as representations of other numbers isn't exactly the easiest idea to wrap your head around, but Adafruit's Collin does his best to explain it. The video walks you through the essentials here, how binary represents decimal, how that's represented in hexadecimal and why exactly computers need all that to begin with. This is all useful if you're starting out programming or you're just curious about why computer code looks the way it does. The video's a bit old so you might have caught it when it first came out a couple of years ago, but if not, it's an excellent explanation of how binary and hex work.
Collin's Lab: Binary and Hex [YouTube]