Good question. At the brake fluid resovoir
ADD BRAKE FLUID
You open the hood, find the brake fluid reservoir, take the cap off and add DOT 3 brake fluid up to the full level.
You can add brake fluid inside the brake fluid reservoir. The reservoir is located on the driver's side under the micro-filter panel.
Locate the brake fluid reservoir, and pour brake fluid in until it's at the appropriate level.
Brake fluid reservoir is located on the firewall next to the steering column. Remove cover top of master cylinder to add brake fluid.
It does not make a difference if the car is hot or cold when you add brake fluid.
The red brake light indicates that the parking brake is on or that the brake fluid is low. Be sure to add the specified brake fluid if you add fluid. Also make sure that you don't allow any dirt to get into the brake fluid and don't overfill the brake fluid either.
The low brake fluid signal on a Chevy Cavalier indicates that the brake fluid level is below the recommended level. It is important to add brake fluid immediately to prevent brake system failure, which can result in loss of braking power. Check for leaks in the brake system when topping up the brake fluid.
Add 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.
It uses brake fluid in the brake fluid reservoir. The clutch fluid (brake fluid) is fed by the brake fluid reservoir. The clutch fluid reservoir is just beneath the brake fluid reservoir. So, add fluid to the brake fluid reservoir to fill the clutch fluid, also.