Ineed finding out what a circuit is?

Well it really depends on what circuit, there's a circuit that means... hmm

ill try to give an example,
You're at a race track, and usually race tracks have the start line, and the finish line, usually they're the same line. So basically where I'm getting at is, it starts where it finishes in circular route; if that made any sense. 

It could also mean simple transportation from one place or another. 

Yes you are correct use the scientific method