Best way to edit multi screen footage into one clip.
Adobe Premiere Pro actually has a multicamera mode you can use where it will display all the videos playing together and you can switch between them.  You just line up the time and then can swap.  If they aren't time synced, then you can simply cut clips out and place them at will.  That's why it is called non-linear editing (NLE), because you can take clips and put them together without having to work linearly (deck to deck) like you used to.

While links are generally discouraged, I think this link to Adobe's help pages is probably the most ideal explanation of how to do multicamera editing.