A Garganta literally tears open the dimensional fabric separating the worlds, revealing a tunnel of whirling, torrential energy that must be focused and solidified to create a discernible pathway. It is primarily used by Hollow and Arrancar, but some other characters have used it through different means.
There is also another use for Garganta, only shown once: Garganta Broadcast, a visual broadcast similar to a television screen, created by using individual Garganta portals. Ulquiorra Cifer does this in order to show the current predicament of Orihime Inoue's friends (Ichigo Kurosaki, Toshiro Hitsugaya and Rangiku Matsumoto) fighting their respective battles. It is unknown if he could create as many as desired, or if three broadcasts are his limit.
Kisuke Urahara is the only person to use an incantation for this technique. The incantation he used is: "My right hand is the stone that bridges worlds. My left hand is the blade that binds reality. The black-haired shepherd is hung from a chair. Stratus clouds come, and I strike down the ibis".
This technique appears to be native to all Hollows, Arrancar and Espada in general. In addition, Souke Aizen, Kaname Tosen and Kisuke Urahara have shown the ability to manipulate the Garganta. More recently, Captain Mayuri Kurotsuchi has acquired the ability to use Garganta through extensive research whilst trapped in Hueco Mundo.