In short, the lens names state the speed of the lens, the maximum aperture. A Summicron is always a lens with f2, a Summilux has f1,4 etc.pp.

Erwin Puts used to host a free (and limited) copy of his Leica Lens Compendium:

He removed it while he is working on a new edition, but has it archived:*/http://.../llcforweb.pdf

It will help you a bit with your endavour.