What is Visual Effects?

Visual effects (commonly shortened to Visual FX or VFX) is the term used to describe any imagery created, altered, or enhanced for a film or other moving media that cannot be accomplished during live-action shooting

Why are visual effects important?
These days VFX is the most advanced technology used in movies to give the scene a more realistic look.Visual effects involve the integration of live-action footage and generated imagery to create environments which look realistic, but would be dangerous, expensive, impractical, or simply impossible to capture on film.
How will visual effects help with my video?