Fill Flash

The second typical shooting situation is to use the flash in bright ambient light to lighten up shadows, typically for subjects getting direct sunlight that produces harsh shadows.

sample photo 2 without and with fill flashOn the left Freddy has taken a seat in the garden on a sunny day for a photo without and one with fill flash (click to enlarge).

To take pictures of people direct sunlight is normally unfavorable, the sample image has small overexposed areas although it is already taken with an exposure compensation of -0.7.
It would have been better to move to a another place with more balanced light, tweaking camera settings cannot produce great photos from bad light.

sample photo 3 without and with fill flashHere another example, better suited because the subject does not have these bright reflections: The shadows in the second picture are a lot brighter because of the fill flash, getting already a slightly unnatural look.
We will adjust this later with flash compensation.

A very similar case is to that your main subject is completely in the shadow in front of brighter background and the whole subject needs to be lightend up:

sample photos without and with fill flash