For the vast majority of vehicles, a single fluid - brake fluid - is used in both the clutch and brake reservoirs. Check the cap of your clutch fluid reservoir - it should indicate if you need a special fluid.
Brake fluid should be changed every 1 or 2 years. Over time, moisture diffuses into the fluid through brake hoses and rubber seals, increasing the water content. If your brake fluid is low, you probably have a problem such as a leak. Leaks and excessive moisture in the fluid can both result is a loss of hydraulic pressure and braking ability, so it's as well to check and change your fluid periodically.