Here is a good place to start: Modern Firearms - Rifle - Tokarev SVT-38 SVT-40 I really enjoy that site, it has data on a great many weapons from all over the place.
Here is a "how it works" break down. Scan taken from Small Arms of the World 11th Ed. by Edward Ezell/W.H.B. Smith .
Another thing about the SVT, the Nazis copied its gas reloading system in their Kar-43. It was much superior to the Danish Bang (that is the gunsmith's name, S. Bang) design both the Walther and Mauser versions of an autoloading rifle they themselves had built.