Could someone explain the line by line tactic? I never understood it.
I've never found a good source for it, but I've read that Francis Swamp Fox Marion was the father of guerilla warfare/ special operations in the US. By that I mean, he used unconventional tactics like not waiting in line to be shot in the face, and attacking at night in small groups on the flanks, or assassination of officers then retreating.
The following entries in the FAQ might be of use to you:
http://www.reddit.com/r/AskHistorians/comments/1tynhz/how_prolific_was_guerrilla_warfare_during_the/
/u/reginaldaugustus, /u/BeondtheGrave and /u/Rittermeister give some good answers that are applicable to your question.
The best concept of "special forces" in the Revolutionary War would be people like "Morgan's Riflemen" or any other group of men that had vast experience with the musket and could work as light infantry skirmishers. (Usually hunters and frontiersmen)
The concept of line by line is simple. Due to the inaccuracy of the musket a commander could deliver the most damage by having his men launch fires in volleys. The reason they stood shoulder to shoulder in close squares (opposed to spread out) is that with the smoke from the hundreds of guns firing the odds of you hitting one of your own men would have been far too high.