It's a redstone clock. Basically, it alternates the current so you can repeatedly activate certain functions.
You know item dispensers? Well, say you want them to shoot arrows, eggs or whatnot continuosly. Well, hook it up to a clock, like mine, and you do that.
Clocks work on delays, or ticks. A torch delay is one tick, and a repeater can be set between 1 and 4 ticks. This means that if you have a loop, the delay will update one part of the circuit to be powered while the other one powers down. This is easy to visualize if you're doing it in a loop on the ground.
When you want to make it one wide, you have to take advantage of other properties of redstone. Repeaters take power from a block and can send it into another block. Because repeaters also control the direction a signal flows, we can send a signal down and up in the directions we want, controlling the way the signal alternates.
I'll probably just make another video tomorrow where I'm not mumbling. I might make a video where I explain some properties of redstone as well.
The main problem right now is that I don't own the computer I'm using (my dad's iMac), and that the software to record it costs $99 bucks. That's just to get rid of the watermark. I'd be okay with buying it if I was sure I'd get a mac next, but ig I end up getting a PC, I'd have to get fraps. Better to just wait until I get myself a computer.