A reflector is used for fixing odd shadows. It does not create light but bounces light that already exist. Reflectors are a good tool to be used outside. In a studio you have electricity and you can make a lighting setup as you desire. Outside you do not have this at your disposal unless you have a crew building a film set for a whole week and a generator running in the background. Therefore the reflector can be used to reflect the sunlight to lighten up your subject from an angle the sun does not.
In Blender you can create light where only the sky is the limit, so, if I were you, I should forget this whole reflector idea. (In Blender that is.)
The background is also a way to lighten up your scene. If you don’t want that, you leave it black.
Lighting is a serious topic on its own. Check out Gleb Alexandrov’s YT channel https://www.youtube.com/channel/UCVA3cYOgsTN4hs3v7pjne7w
