First off I'll start by saying, if you buy a cheap amp kit it's going to come with cheap components. The one I have shown in the picture(1) is made by Pheonix Gold which will probably cost you around $50. Of course you could save $30 and buy that $20 amp install kit, but I wouldn't reccommend it. You can also buy the parts individually. In the picture I have a amp kit as well as the individual components which I will give a brief discription of.

1.  Amplifier Installation Kit: contains all parts necessary to install a amplifier.

2.  Power, Ground, & Remote Cable: The power cable (red)is ran from the battery to the amplifier. To run the power cable you will either have to find an unused grommet(black rubber plug) in the fire wall or you will have to drill a new hole. In most cars you should have no trouble finding one. When you find one, pull it out and punch a hole through it large enough to fit the power wire through. You could also use a small amount of silicon to seal the hole. This way you will have a water tight fit when you put the wire in. The ground cable(black) is ran from the amp to a ground point on the car. The ground wire shouldn't be any longer than 24 inches. If possible try to use a pre-exsisting bolt to ground the wire. Wheither you find a suitable bolt to use or if you have to drill a new hole, make sure you remove any paint to ensure good grounding. Depending on how much current the amp draws, you will need a certain gauge wire. Here is a wire gauge chart. The remote wire(usually blue) is ran from the remote wire on the head unit to the remote wire connection on the amp. This wire is responsible for turning the amp on and off when ever the head unit is on/off.

3.  RCA Cables: This cable is used to carry the audio signal from head unit/equalizer/or electronic crossover to the amplifier. The RCA cable should be ran seperately from the power wire to avoid possible noise issues. If you are installing the amp in your trunk you will most likely need a 20 ft. cable.

4.  Battery Termianl Connector: These will usually have to be bought seperate from the install kit and will cost around $15 & up. Most of these are gold plated to decrease resistance.

5.  Battery Terminal adapters:  These are required for side mount batteries commonly found in compact cars.

6.  Inline Fuse Holder: This is placed inline with the power cable no further than a 1 foot from the battery. The further it is from the battery the more chance there is for an electrical fire to happen. One of these is included with most kits. The purpose of this fuse holder is not to protect the amp, it's purpose is to protect the wire incase of a short between the battery and the amp.

7.  Solderless Connectors: These are used to connect power and ground cables to the battery, amp, and grounding point. They are connected to the wire by either crimping them or by a set screw.

8.  Split Wire Loom: This is a corrugated tubing with a split down its center through which wires are placed. It protects wire that is ran under the carpent, in the trunk, and under the hood, from damage. You have most likely seen this ran throughout your car. Most amp kits I've seen either dont come with it or they dont come with enough. A lot of the kits I've seen only come with enough loom to protect the wire thats ran under the hood(about 5ft.). Wire loom should be used along the entire run of the power cable, RCA cable, speaker cable and so on and so on. I know I've spent over $100 in cables and I dont wanna have to replace any of them.