In my opinion, Idris had the best answer. Shadowsreached was too vague and her answer was convoluted.
You should look up what's called the "Sunny 16 Rule". It's a guideline for how to take pictures outside with manual exposure. The same principles apply whether you are using film or a digital camera.
There are 4 basic things you absolutely need to know and understand - ISO, aperture, shutter speed, and depth of field.
The first is what's called ISO. That means light sensitivity. A higher ISO rating means more light sensitivity, and a lower ISO means less light sensitivity. So 400 ISO is more sensitive to light than 200 ISO. If you are using film, the number you see labeled on the film is the ISO rating. Sometimes they call it the "film speed" but that isn't really an accurate term to use. It's better just to say ISO rating.
The next thing you need to understand is the aperture. The aperture is the opening on the lens which lets light in to the camera. It has settings called "F-stops." If you are using a manual camera, there will be a dial or knob on the lens to change the F-stop. Think of the aperture as like the iris in your eye. You can use different F-stops to let in more or less light. It's a little confusing at first, but a smaller F-stop number actually means a bigger aperture. That's because it's a ratio. So f/3.5 is bigger than f/8. The aperture will go down to F/16 and some cameras will go down to F/22 or even F/32.
The next thing you need to understand is the shutter speed. The shutter speed means how long the shutter will stay open when you press the button. It's usually measured in fractions of a second, like 1/200. A smaller number means a slower shutter speed. A slower shutter speed will mean a longer exposure. A faster shutter speed will mean a shorter exposure.
The shutter speed and aperture setting both determine the overall exposure of the picture...how "light" or "dark" it will be. Basically, you set the aperture and shutter speed to have a certain amount of light for a certain period of time.
The "Sunny 16 Rule" says that if you are taking pictures outside on a clear sunny day, you should set your shutter speed to the same as the ISO of your film, and set the aperture to f/16. You will adjust the aperture to the lighting conditions. So if it's a little hazy or partly cloudy, then you might want to open up the aperture to f/11. If you're in the shade, you will open the aperture to f/8 to let in more light. You can also leave the aperture at the same setting and change the shutter speed, but that can be a little tricky.
If you are using a digital camera, the same rule applies. Set the shutter speed to the same as the ISO. But of course, that only works if you are using a camera that has completely manual settings.
The other thing you need to understand is what's called the "Depth of Field." The depth of field means the distance in front and behind your subject that will be in focus. It's an optical effect. With a long depth of field, everything will be sharp. With a shallow depth of field, the subject will be in focus, but the background will be softened and blurry. When you change the F-stop, that changes the aperture and how much light comes in to the camera...but it also changes the depth of field. A bigger aperture (like f/8 or f/5.6) will have a more shallow depth of field. Sometimes that's useful for when you want to blur out the background and draw more attention to something in the foreground. A small aperture, like f/16 will make everything sharp. Usually, for landscape photos you want a long depth of field and you want everything to be in focus.
So that's basically what you need to know for now. Look up ISO, shutter speed, aperture, and depth of field.
What Idris said about negatives is true. You can tell whether film was correctly exposed by how the negatives look. But you can learn about that later on, if you decide to learn about film photography. (By the way you should, you can learn a LOT more about photography with a manual film camera).