You've got it all wrong, liquids can't be compressed - only pressurized. Gases OTOH can be compressed. It's like the difference between poking at something with a stiff rod, or with a sponge. With a liquid, whatever force you put in at one end is what you get out at the other - just what you want if you're planning to build a closely controlled system like brakes.
Liquids in hydraulic brakes help to stop an automobile by creating pressure and moving a set of pistons to generate force. This force is applied outward and causes friction that stops the automobile.
Volume!
Because liquids can't be compressed. Whatever movement you put in at one end you get back at the other. Gasses can be compressed, like a spring, which is kinda awkward if you want to build something that can be closely controlled.
hydraulic oil
depends on the type. There are hydraulic bike brakes, but most are mechanical.
No. Hydraulic brakes can be either drum or disc brakes, and these two brake types are available as air brakes and air-over-hydraulic systems, as well.
It was 1939 that Ford started to use hydraulic brakes.
Depends. Most bikes don't have any hydraulic components, but some have hydraulic brakes. Usually disc brakes, but there are at least two models of hydraulic rim brakes as well. And it could easily be argued that suspension bikes with oil shocks are hydraulic in design.
Brakes that are actuated by a hydraulic fluid (such as brake fluid). Other types are air over hydraulic (air actuates hydraulics) and pneumatic (air) brakes.
Compressed air.
We would need to know what type of brakes you have... S-cam air brakes, air disc brakes, air piston brakes, air wedge brakes, hydraulic drum brakes, hydraulic disc brakes... they're all different.
No, they use air pressure or actually the lack of air pressure to stop the vehicle. The brakes are fully on until pressure builds up in the tank releasing the brakes. When you push the brake pedal this removes air from the system and applies the brakes.