Stargate is a 1994 French/American science fiction movie created by Dean Devlin and Roland Emmerich. This movie started the Stargate franchise which went on to spawn several TV shows and their own related movies.
After the discovery of the Stargate and finally getting it to work, a team travel across the known universe to another planet to determine if we're alone in the universe and if they're a threat. The stargate creates a connection with another stargate by creating a wormhole between them. Stepping into the stargate transports you to the other stargate almost instantaneously.
The Stargate franchise began with the movie "Stargate". The "Stargate: SG1" series starts several years after the events of the first movie and ran for 10 seasons. The movies "Stargate: Continuom" and "Stargate: The Arc of Truth" wrap up the main story lines of the series. The "Stargate: Atlantis" and "Stargate: Universe" series are both spin-offs of the main series and ran for 5 and 2 seasons respectively.