As you probably know, trucks are the metal axles on your skateboard that enable you to turn. I will try to explain thoroughly in this guide all of what you need to know.
First, trucks will probably last you the longest out of any component on your skateboard. You may need to replace parts occasionally, but they tend to take a lot of wear and tear. You are going to want to replace your bushings when they crack. Bushings are the small, plastic objects on the inner part of the truck, to replace them, unscrew the kingpin bolt, and take them off the kingpin, setting the new ones on. Your kingpin may also need replacing. The kingpin is the long bolt the bushings go on. Both of these replacements are relatively inexpensive.
Another common problem with new trucks is them only turning one way. You may be worried about this problem, but it will go away. Theproblem is that the bushings haven't been worn in, and will have a tendency to lean a certain way. It will go away soon enough.
One of the most common problems, however, is the ends of the trucks getting worn down by landing in primo. For about 20 dollars USD, you can buy a reflex utatool. This tool has an axle rethreader, which will fix the problem.
Trucks are very diverse. Some have add ons that will make them last longer, some are not very good. I will cover some of the popular add ons in trucks.
Tensor-These trucks have a built in slider piece that will make bluntslides, noseslide, noseblunts, and anything relying on the nose or tail longer.
Destructos-These are "made with the best aluminum on the market." Besides that, they are average trucks, most people like them.
Fury-These are average trucks, there's nothing very special, but they are long lasting.
Grind King-These trucks have numerous interesting and unusual designs. They come in low, mid, and high, so you can choose what you like.
Independent-These are some of the best trucks out there. Nothing fancy, just great trucks.
Krux-These are similar to Indys, except they come in mids and lows, and have numerous designs, such as wood grain and Krux Ice.
Hopefully, I have covered the basics of trucks, so you know a little more. Good luck out there, and go skate!