A list of parts necessary for a working scooter
1.The first part you should need is the handle bars. The handle bars are usually one piece, from the forks to the grips. Occasionally, on the lower-grade scooters, you will find that the grips are on seperate pieces that is usually held in by a button to he rest of the bars.
2.The next thing you will need is the headset. the headset consists of the bearings around where you screw the handlebars to the forks, and their coverings. You can get compression or threadless headsets, as well as threaded ones.
3.The third part is the forks. Depending on the type of headset you have(compression or threaded) you need o get either threaded or compression forks. Threaded forks are easier when it comes to assembly, but compression are better for all-around performance. 
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4.The next necessary part is the deck. Obviously, the deck is the part on which your feet go on as you ride. The forks and headset go through the front of the deck, griptape goes over the top of it and the rear wheel's forks are on the back end.
5.The last necessary part, is the wheel. You need a wheel on both the front and rear forks if you want your scooter to move. The wheel has a bearing on each of its sides, and a metal spacer between them. Wheels are put on by placing them in the forks and placing the axel through the forks, bearings, and wheel. Wheels should be replaced if cracked, bent, or a flat spot is found.
A list of parts that are not necessary, but very useful!
1.A first unnecessary part is the grips. Grpis make landings more comfortable, and help you keep a solid grip on your bars.
2.The next part is griptape. Griptape keeps your feet from sliding around on the deck, and adds alot of value to how cool your scooter looks.
3.The third part is pegs. Pegs are put on the outside of the wheel, and can be useful when doing certain grinds, and must be present for certain tricks such as the icepick.
4. A fourth and final part is the brake. It can be used for doing tire stalls and other such tricks. It also slows you down gently and keeps your feet from getting caught in the wheel.
