A repeat of an older post here – because it is very important.

When you use flash, you can either combine it with existing light (as in a party) or not (as in a studio, or as in a snapshot).

To hep you understand this, here is a representation of when you do, and when you don’t, use flash; and when you do, and when you don’t, combine it with other light:

If you want to be a creative photographer, you should probably practice the three types on the right.