It's recommended to check your car's fluids periodically to ensure the fluids are clean and at a sufficient level.
Most cars have a dipstick in the engine bay that lets you quickly inspect the oil. It's best to check your oil after your engine has turned off and the oil has settled at the bottom.
See if the coolant falls between the minimum and maximum indicators on your coolant expansion tank. If it doesn't, open the radiator cap to see the same.
You can remove the dipstick and check the markings on the reservoir. If the fluid is low, top it off.
Most cars have a brake fluid reservoir in the engine bay. You can check it is by taking a look at its level and color.
If you are unable to check the fluid, seek a professional mechanic to inspect the fluid condition.