Multicam editing is when footage of the same event is recorded with different cameras and then edited together into a single video.
As of VEGAS Pro 8, multicam editing is made possible in VEGAS with a new multicam mode.
To perform multicam editing in VEGAS, follow these steps:

1. Add each video to a track of its own in the timeline. Pre-synchronize the video events as much as you can.
2. Select the header of each track you want to use in multicam mode. 
3. Go to "Tools" > "Multicamera" > "Create Multicamera Track". All the video events in each multicam track will now be combined into a single destination track.
4. Go to "Tools" > "Multicamera" > "Enable Multicamera Editing". The preview window will be divided into different sections. Each section contains one camera event and is labeled with a number in the bottom right-hand corner.
5. Place the play cursor at the beginning of the timeline and start playback. 
6. During playback, the numbers on your keyboard correspond to the camera events in the preview window. Pressing a number switches the video to that camera. You can use this technique to edit together your destination track live during playback using the footage from all your source tracks.

For more information about multicam editing, go to "Help" > "Contents and Index" and enter "multicamera" in the "Index" tab to go directly to the corresponding help section.