Generally brake fluid.
DOT (3) brake fluid
This depends on what type of vehicle that you have. But in most vehicles you would add the brake fluid to the master cylinder. This can be located on the firewall of your vehicle. Do not confuse a clutch master cylinder with the brake.Make sure you add the fluid to the brake cylinder.
DOT 3 Brake fluid.
The fluid for the clutch comes from the brake fluid. After the brake master cylinder, there is a clutch master cylinder which takes fluid from the brakes. Fill up the Brake master cylinder.
dot 3 or dot 4 break fluid
If you look on the cap covering the master cylinder it will list the correct fluid.
Look to see where you fill the brake fluid and where your filling the brake fluid that is the master cylinder.
The clutch gets its fluid from the master brake cylinder reservoir. The master clutch cylinder sits just below the master brake cylinder reservoir and is fed fluid by gravity.
There is no fluid in the clutch....The clutch master cylinder takes DOT 3 brake fluid. It is the same fluid that you put into the brake master cylinder
In the master cylinder
If a pressure type brake fluid dispenser is available attach it to the top of the master cylinder. Other wise fill the master cylinder, start with the wheel cylinder that is furthermost from the master, and bleed until fluid comes out clean and free from bubbles. make sure to replenish the the master cylinder as needed. then proceed to the next farther wheel cylinder and repeat with the rest of the wheel cylinders. top off the master cylinder. Test with the engine off then with the engine running before driving.
Most vehicles have master cylinder reservoirs that you can see the fluid through. The side of the reservoir has a high and low fluid mark on it.