The Stechkin automatic pistol was adopted by the Soviet military in 1951, alongside the Makarov pistol. Both are chambered bot the 9x18mm Russian cartridge, and both use simple blowback mechanisms. The Stechkin is a heavier and bulkier pistol, though, as it is designed for fully automatic fire.
The Stechkin uses a 20-round magazine as standard, and has a selector switch allowing single shots or automatic. It was originally issued with a combination shoulder stock/holster (much like the Mauser 1896) to allow more precise shooting, and was supplied to support troops like tankers, RPG carriers, and artillerymen. It became apparent, however, that a machine pistol was not a particularly practical weapon, and the Stechkin was slowly withdrawn from use. The weapon received a bit of new life in the 70s, when some existing stocks were updated for Spetsnaz use, with the addition of sire stocks, threaded barrels, and sound suppressors.
Over in the Vault page on the Stechkin we have a copy of a Russian manual on the piece from 1960, as well as a US government official translation of it into English, for folks who would like more details.