Trucks
Trucks, or axles, are what hold the wheels on the board. They are a very durable part of your complete they are the surface you grind on, and they allow you to turn. To know about them is pretty important, so lets get started: There are four major parts to a truck, the hangar/axle, kingpin, bushing, and the base plate.
The base plate is the part that gets fastened to your board (important note: when putting your trucks on, kingpins face in!!!!! if you don't do this, then you will lean one way and turn another! You will fall!!) The kingpin is the big bolt that comes up through the base plate. This is the bolt that you can adjust to make your trucks looser or tighter. It is also the part of the truck that tends to break the most. It's a pain in the ass, but they can be replaced. The bushings, or pivot bushings, are what the kingpin tightens down. They come in a few different hardnesses. With use and abuse, these will crack. After they crack, they are difficult to keep tight. Fortunatley, Shorty's and a few other companies sell replacement bushings that differ in hardness, so you can customize your trucks so that they are comfortable for you. The hangar is the last piece of the puzzle. It's the part you grind on. It interlocks around the kingpin and bushings. The thing that sticks out from either side is the axle (it's where your wheels go, eh?). A common problem with trucks is a problem known as "axle slip". This is when you try to kick flip, and land 'primo' (see skate glossary), and your axle slips (duh), resulting in one locked wheel, and one loose wheel. Axle slip sucks. If you don't have a skate tool on you, and this happens, you can temporarily fix it by banging it back into place. Fair warning, though, this just makes it worse in the long run.
Don't let anyone tell you how to ride your trucks, in fact, don't even listen to them. Find out what is comfortable for you. Some people like really tight trucks, some people like loose trucks. It differs person-to-person. I will say, though, that many people like them loose for carving, but a bit tighter for flip tricks (it's a bit easier to balance with slightly tight trucks, but its very important to be able to turn). A popular style is to keep the back truck slightly tighter, for ollie stability, but it's all up to you. And that's the beauty of it all.
Of course, one of the biggest factors in determining which trucks to get is the weight. Nobody wants heavy trucks, or do they? Some companies have created ways to lighten the weight of the truck, while keeping the durability. Grind Kings and Thunders are on the lighter side, while Independent and Destroyer are heavier. Keep in mind that almost all trucks fall between 10 and 13 ounces. If you really think that taking six ounces off your board will make you skate better, go for it. But maybe you should close your eyes and see if you can tell the difference. Most trucks are available in a few different widths, as well. Which one is right for you? Well, if it's too big, you'll look like a turtle, and if its too small, you won't be able to see them while riding. Your truck bolts should be flush with your board, so it depends on what size board you ride. Get it?
In the past few years, there have been many different variations on trucks, to provide a bit of diversity to your board. For example, Tensor Trucks offer a plastic piece in the base plate, to assist with tricks like nose slides and tail slides. Many manufacturers offer their trucks in both "hi" and "low", meaning a raised or lowered kingpin, which can affect overall grinding area. Some companies offer a non-slip axle guarantee. Like shoes, your trucks may take a few days to 'break in' properly, or for you to get used to them. Once they are broken in, though, you will get a feel for what you like and what you don't like. If it ain't broke, don't fix it.