Most, if not all, vehicles on the road today have a brake fluid reservoir that allows you to see through so you can check the fluid level without opening the cap. The brake fluid reservoir will be located toward the back of the engine bay on the driver's side, up high where it's easy to access.
Once you locate the brake fluid reservoir, you will see markings on the side that tell you if you need to add any brake fluid. You may need to clean off a little road grime to see the marks clearly.
If you do need to add some brake fluid, be sure to follow these tips.