By Beyond the Stargate:
Finding a Ancient outpost in Antarctica, on Earth, we have been trying piece together the clues to finding the Ancient city, as said in many ancient legends. When Dr. Daniel Jackson figures out the Stargate address, a team of the brightest people in the world is established to explore this ancient city. The planet on which Atlantis lies is far away, but not out of reach. A powerful power source, know as a ZPM is used to connect to the Stargate and establish a wormhole to this great city. Having only one ZPM, the Atlantis team embarks to this Ancient city, know that they could never return. They have hope of finding technology to help humans fight against the Gua'ud, and obtain greater knowledge then the one we already have, but most importantly find another power source and returning home with this knowledge. Little did they know, of the wonders and mysteries of the Pegasus galaxy, and the enemy, that once slept will awaken, and will stop at nothing to get to Earth.

By Scifi.com:
When a secret base abandoned by the Ancients — the original builders of the stargates — is found buried in the ice of Antarctica, the Stargate Atlantis team is recruited for the most daring stargate mission yet: a one-way expedition to the distant Pegasus galaxy.

There the Stargate Atlantis team encounters a number of primitive human civilizations ... as well as the Wraith, a sinister new enemy that threatens human life everywhere.

The Stargate Atlantis mission is headed by Dr. Elizabeth Weir (Torri Higginson), a specialist in diplomatic relations. Her political savvy is balanced by the go-with-your-gut bravado of her military counterpart, Maj. John Sheppard (Joe Flanigan), a courageous and gifted pilot. Rounding out the team are Lt. Aiden Ford (Rainbow Sun Francks), the enthusiastic young officer who becomes Sheppard's second-in-command; and Dr. Rodney McKay (David Hewlett), a clever and quick-witted astrophysicist with previous experience at Stargate Command. The team is befriended by Pegasus galaxy native Teyla (Rachel Luttrell), a beautiful young leader among the Athosian people, with whom the Atlantis team has forged an uneasy alliance against the Wraith.

Rounding out Team Atlantis are Ronon Dex (Jason Momoa), a human native to the Pegasus galaxy who has fought the Wraith for seven years in defense of his planet; and, from Earth, Col. Steven Caldwell (Mitch Pileggi), the commander of Earth's newest intergalactic battle cruiser, the Daedalus.