For those who are confused about what a non-linear editing program is it should come as some relief that it is not nearly as complicated as it sounds. Video editing can be a difficult proposition to someone who has never tried it, especially when they do not even have a basic understanding of how this system works. Here are a few basics about non-linear video editing.
Non-linear editing is in opposition to linear editing. Linear editing was the original editing system, where actual pieces of film stock where cut and 
spliced together to make the final film. What this meant is essentially that you had to go through the film, making the edits, and could not go back and change them. You had the ability to preview the changes, but if you wanted to go back you were really out of luck.
The non-linear system changed this and turned editing essentially into a file storage and reference system. With a non-linear editing system, which is really just editing software, you capture or import all of your media and then the program references it for film construction. You can cut together and alter whatever you want and it is not permanent, although you can save your changes to the final film. No changes you make permanently alter the source material.
Image: http://www.flickr.com/photos/adpowers/8045962/
The editing software you are using will save your project file, as well as all of the media and changes you have made. Every time you open the project the program references the source media, but then fills it in to the construction you have made in the program. Even though you have only used snippets of each full video clip you have captured, the program still references that so the media can appear in the project. The ability to save and close the projects means that you can go back to it whenever you like.