The Chassis of your ship holds all the components together. It has a maximum mass, maximum hitpoints, both experimentable, plus fixed roll/pitch/yaw/acceleration/deceleration characteristics. Some ships are available in different styles, and all non-Imperial craft can be painted and textured using kits.
When your shields and armour have been breached, your chassis and components will take damage simultaneously.
Once your chassis gets to 0 your ship will explode.
Ship chassis decays just like any other component. Therefore, once you've died lots of times and your maximum hitpoints get to a low level, you will find your ship explodes almost as soon as you lose shields and armour!
When creating a chassis the Shipwright is able to experiment on hitpoints and mass. Typically they will be experimented for maximum mass; the exception being the POB ships (YT-1300 etc) which currently have just under 5m mass (not sure if this is a bug or not) so usually these will be entirely hitpoint experimented.
Buying a chassis involves buying a set of "blueprints" first and then taking these blueprints to a chassis dealer at a starport. All of the large starports have them, and they pop up on the overhead map when you're outside of the starport. They will ask you to see the blueprints and then generate the ship in that starports hanger. You can then access it through the starship terminal.
Experimentation: Mass. MA, OQ, ST, UT. Hitpoints: HR, OQ, ST, UT
Tier 0 ships (2k steel, 2k low grade ore, 1k aluminum) Syck, Z-95 Headhunter, TIE Light Duty
Tier 1 ships (7k steel, 4k low grade ore, 2k aluminum, 2k inert petrochem) Dunelizard, Y-Wing, TIE Fighter
Tier 2 ships (12k steel, 6k low grade ore, 6k aluminum, 3k inert petrochem, 3k iron, 3k fiberplast) Kihraxz, Kimogila, Y-Wing Longprobe, TIE/In
Tier 3 ships (24k steel, 12k low grade ore, 6k aluminum, 6k inert petrochem, 6k iron, 6k fiberplast) Ixiyen, X-Wing, TIE Bomber, TIE Interceptor
Tier 4 ships (32k steel, 16k low grade ore, 8k aluminum, 8k inert petrochem, 8k iron, 8k fiberplast) Rihkxyrk, A-Wing, TIE Advanced, TIE Aggressor
Tier 5 ships (70k steel, 20k low grade ore, 10k aluminum, 10k inert petrochem, 10k iron, 10k fiberplast, 10k siliclastic ore, 10k copper) KSE Firespray, YT-1300, B-Wing, YKL-37R Nova Courier, TIE-Oppressor, VT-49 Decimator
Buying Guide Edit
The buying guide for chassis is simple. If you're grinding, buy the cheapest chassis you can. Once you become more interested in squeezing every last bit of performance out of your ship, you can become more concerned with mass. The are really only 2 ships that come to mind where I would recommend really going all out for a high mass chassis, and those are the A-wing and the tie advanced. Because of the way chassis experimentation works, it takes an excruciating amount of effort to raise mass even a few hundred points above the 85% experimentation mark. Master level pilots will want high mass KSE's, B-wings, Tie Oppressors, but here the mass allotment is generous as well. If you can't kit out a 211k mass KSE, it's pretty unlikely that you'll be able to go far with a 213k mass, and the price difference is going to be millions of credits.