The guru bead is the bead that the strand begins and ends at, and by convention it is held rather than passed over, which is why a single larger bead sits there. Using a different material makes it findable by touch, and jade is a common choice because it is smooth and cool against the fingers.
On the wood: "rosewood" covers a number of species across several genera, and traded timber is required to carry a botanical name. We print the actual species on the tag rather than leaving the trade name unexplained, because using the term loosely is how dalbergia species end up in products without anyone knowing which one.
Rosewood does not need oiling. It has enough natural oil to take on a sheen from handling, and adding oil to a dense wood tends to attract dust and dull the surface rather than improve it.