SOOOO . . . .

I was looking into the different types of garter snakes there are and it's really confusing but I really want to be able to tell the different species and subspecies apart. I can't even figure out

So Thamnophis means Garter snake which is the genus?

And Sirtalis, Radix and Butleri is the species?

Sirtalis is what? Radix is plains? Butleri is butlers?

Marcianus is checkered but is that the species or subspecies and if it's the subspecies then what is the species? And why is Marcianus sometimes repeated after Thamnophis? Like Thamnophis cyrtopsis cyrtopsis (which is an eastern blacknecked garter snake . . . right?)

Does anyone know of any websites that would help me out please?

Also some pictures of snakes and their normal and Greek (I think it is) names would be a massive help!