Visual Effects is a really broad term that with a lot of techniques.
It's about adding, hiding or removing elements to enhance live action shots. I do tracking, match image, add new elements, create special effects (computer based) and more.
In this commercial for the company Wee made by Absurd Film, I had to remove a huge crane, make falling mini crane and different impacts adding smoke and debris. It even won an award for best commercial, called Gullsild.
This video, a Star Wars tribute were done with Absurd Film. They made everything in less then two weeks, from idea, story, filming, editing to finished video. My part were everything 3D like the Volkswagen, Tie Fighter, R2D2, Star Destroyer and more. I had to track the footage to get the camera movements and color match the 3D objects to the scene. I also did the color correction and grading (color mood).