Greenscreen

iOS: Greenscreen by Do Ink ($5) or Android: Chromavid (free?) is really all you need.

Greenscreen is all about lighting: 

[1] key light (main, front, lighting the subject)

[2] sidefill, "hair light" (from sides and above)

[3] background light (lighting the Greenscreen to kill shadows and for a balanced green chroma color)

The examples shown are screenshots from Greenscreen by Do Ink but most all programs will be similar.

Greenscreen works by converting the chroma color (usually green) in the top layer into transparency, 

allowing the bottom layer (or background) to show through.