Visit their website at www.detonationfilms.com.
They have tons of effects stock footage and more tutorials!
So how do you make a realistic looking film? Compositing. With compositing you take the footage and add footage on top of that to create something new. The Compositing Demo above from Detonation Films demonstrates basic compositing that is used in every Hollywood film with digital effects.
There are three main compositing tools that you will be using based on footage (what the background is)
1. Chroma Key- Chroma is color, meaning you want to key out (meaning- your making a selection from your video and deleting the part) a color like blue or green. (as seen in the demo above)
2. Luma Key- Luma is brightness, this type of key effects the dark or light values or an image. This is great for images with black or white backgrounds.
3. Transparency Modes- These modes blend two layers of video. Take any two pieces of footage and play with them to see how the combine the two layers. Transparency Modes are also in Photoshop under the layer pallet, photoshop is another quick way to be familiar.
There is a lot to learn about this subject which you can make a whole career in, but this is a start.