i want to know how the plunger work that fit into the slave cylinder?

The plunger compresses the fluid and delivers it pressurized through the line to actuate the rod at the slave cylinder. Sometimes if you have any air trapped in the line while trying to bleed the air from the cylinder you will not create any pressure to bleed the lines. If all componets are new and it wont bleed and work you can try an old trick called back bleeding. Take a trigger type oil can which you can buy at your local parts house or hardware store and fill it with brake fluid. Connect a small rubber hose that will slide over the end of the can and the other end over the bleed nipple make sure you have the nipple loose on the slave cylinder and pump brake fluid backwards up to your clutch master cylinder and this will evacuate any trapped air in the system then you can try to bleed the system normally and you should get pressure to your clutch slave cylinder.If not you may have a bad cylinder.

The system is basically a fluid transfer system, depress the pedal and the piston in the master cylinder displaces fluid into the slave cylinder, as fluid is non compressible it moves the slave cylinder piston as the fluid enters the slave, pushing on the release bearing which depresses the clutch diaphragm releasing the clutch.

https://www.2carpros.com/articles/how-a-brake-system-works

The link should explain it.