It is your child's birthday party outside on a beautiful sunny day. You have rented the pavilion for shade and picnic tables. Of course you would like to commemorate this happy occasion with good pictures. The problem is, all of the people in your pictures are coming out too dark!
What is happening is that your camera reads a lot of light in the background so it "thinks" that it doesn't need flash. Most cameras have a light meter built inside. The meter measures the entire scene to determine which settings it needs to get a well exposed picture.
The default metering system is called "evaluative" or "matrix" metering on most point and shoot cameras and DSLR cameras. This metering system will average out the light in the entire scene. It works very well most of the time to give you beautifully exposed photographs.
The exception is when your background is brighter than your foreground. We call that back lighting. You will need flash if you want your foreground and your background to be exposed properly.
The simple solution is to learn how to force your flash on. Almost every camera, including cell phone cameras have the option to turn the flash on. The flash symbol is a lightning bolt. Most cameras will give you the choice of No flash, Auto flash and Flash. No flash is obvious; the flash will not fire. Auto flash is the default. The flash will only go off if the camera determines it needs more light. When you put the setting to Flash, the flash will fire every time.
On a DSLR, there is usually a little lightning bolt symbol on the front of the camera. Press that button to pop up your flash. If the flash is up on a DSLR camera, it will go off every time. The good news is that the flash has its own light meter so it will measure the scene and work with your camera's settings. It will usually not overexpose (or give too much light to) the image.
The flash on your camera is made to light the first thing it "catches". Turn on your flash and see the people and objects in your pictures exposed properly as well as the background!
One issue you may have with a point and shoot camera; the flash is not very strong so it does not reach very far. You'll have to be fairly close to your subject. How close? Look at the pictures. If it is too dark, even with flash, move closer!