If you've ever photographed someone standing in front of a window, you may have gotten a picture of them as a silhouette even though the background looked fine like the plant picture above. Your camera saw all the bright light coming through the window and set the exposure for that. But your subject wasn't in that light, so it was completely underexposed.
You can remedy this problem and reveal the subject's details by changing the flash to Fill or Force Flash. This causes the flash to fire even in bright light. The flash lights up your subject while leaving the background unaffected just as in the picture of the plant below. (You might need to change your camera to Program mode in order to have access to this flash setting. Check your camera manual.)
You can also use this technique outside when your subject is in the shade and the background is bright with sun or snow. In the picture below, a tree to the left of the shot was shading the cattails in the foreground. The water behind the plants was in sun. Setting the flash to Fill or Force Flash brightened up the cattails, giving a second version of the scene.
It's always a good idea to take two shots when you are learning a new camera control. That way you have a before and after version to compare and can choose the picture you prefer.