How and when is the proper time and way to make a bracha on thunder and lightning?
For thunder, one can choose to make either maaseh bereishis or shekocho u’gevuraso. When making both berachos separately, one for lightning, and another for thunder, one would make maaseh bereishis for lightning, and shekocho u’gevuraso for thunder. Usually, however, one sees/hears them together, and one berachah is made for both.
See Be’er Heitev, Orach Chaim 237:1; Eliyah Rabba explains that unlike lightning, thunder is heard ‘throughout the world,’ making the kocho u’gevuraso blessing a viable alternative to maaseh bereishis; Peri Megadim explains that it is better to make one blessing than two; see also Kitzur Shulchan Aruch 60.