Melissa, a cabinet scraper is a piece of steel with sharp edges. Not knife edges, just 90degree edges, and you use it in both hands, bending it very slightly, and pushing it away from you, tilting it so that the edge on the other side from you scrapes off the surface. Along the grain.
There are other types which have handles, which oddly makes them even harder to control for fine work.
As for using oil finish on a guitar, as I said in my 02:37 post, I haven't, and I wouldn't. Not on the belly.
Love it for other things. You just rub it on until it it looks right.